EDP Sciences logo
Subscriber Authentication Point
Search
Menu
Home All issues Volume 681 (January 2024) A&A, 681 (2024) A7 Full HTML
Open Access
Issue
A&A
Volume 681, January 2024
Article Number A7
Number of page(s) 8
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361/202347412
Published online 22 December 2023

© The Authors 2023

Licence Creative CommonsOpen Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This article is published in open access under the Subscribe to Open model. Subscribe to A&A to support open access publication.

1. Introduction

Galaxies are fundamental building blocks of the Universe. Understanding the evolutionary processes of galaxies requires comprehensive investigation of the interplay between environmental effects, such as interactions, and internal structures, such as bars, oval discs, and spiral arms. In the context of the local Universe, there is a transition occurring in the primary drivers of galactic evolution. In the early Universe, the dominant forces were characterised by violent and rapid processes, such as mergers. However, there is now a discernible shift towards a more gradual restructuring of mass and energy that is attributable to the influence of secular evolution (Kormendy & Kennicutt 2004). Decoding the aspects of a galaxy, such as its gas content, star formation activity, and structural properties, provides valuable insights into its evolution. This understanding can be achieved by recognising the significant impacts exerted by both secular and environmental factors on these crucial galaxy characteristics (Toomre & Toomre 1972; Skibba et al. 2009).

One of the observable parameters that can be used to understand the factors influencing the evolution of a galaxy is the star formation activity. By measuring the star formation rate (SFR) and analysing the spatial distribution of young stars, crucial insights into the evolution of the galaxy can be obtained. The intense ultraviolet (UV) continuum radiation emitted by young massive stars of spectral types O, B, and A serves as a direct indicator of ongoing and recent star formation (Kennicutt 1998). The understanding of star formation goes beyond quantifying the SFR and requires exploration of the underlying mechanisms governing this process. At its core, star formation relies on the presence of cold, neutral gas as the fundamental ingredient. The significance of neutral hydrogen (H I) gas in supporting and sustaining star formation is well established (Doyle & Drinkwater 2006; Leroy et al. 2008; Kennicutt & Evans 2012; Zhou et al. 2018; Parkash et al. 2018). By examining the UV properties of galaxies and by analysing the spatial distribution of H I gas, valuable insights can be gleaned regarding the mechanisms responsible for recent star formation and consequently the evolution of the galaxy. This approach allows us to obtain a comprehensive understanding of the interplay between star formation processes and the presence of neutral hydrogen gas, shedding light on the underlying dynamics shaping galactic evolution.

The galaxy pair NGC 1512/1510 is located on the edge of the Local Volume at a distance of 12.60 Mpc (Tully et al. 2016). The massive barred-spiral galaxy NGC 1512 and its satellite, NGC 1510, a blue compact dwarf (BCD), which are separated by a distance of ∼18.3 kpc, are undergoing an interaction that started about 400 Myr ago (Koribalski & López-Sánchez 2009). NGC 1512 hosts a strong bar (bar strength, Qb ∼ 0.27, Buta et al. 2005, 2006), which might have formed as a result of interactions (Koribalski & López-Sánchez 2009). This galaxy hosts a circumnuclear ring of ∼16″ × 12″ in diameter that shows intense starbursts. The galaxy also hosts an oval inner ring of 3′ × 2′ in diameter, which is elongated along the major axis of the bar (with the relative angle between the bar and inner major axis ≳10°; Maoz et al. 2001; Meurer et al. 2006). The inner ring is notable for its sharp definition due to an enhanced degree of star formation (Hawarden et al. 1979). The galaxy has spiral arms wound around it, with one of the arms disrupted, possibly due to its interaction with NGC 1510. Studies have also discussed the possibility of arms being formed due to tidal interactions (Kinman 1978; Ducci et al. 2014). The properties of the galaxy pair are listed in Table 1. We identify NGC 1512 as the main galaxy and NGC 1510 as the satellite galaxy, based on their mass ratio of 50:1 (Chakrabarti et al. 2011). The galaxy NGC 1512 is therefore an excellent target for our investigation, as it offers a compelling opportunity to study the combined effects of environmental and secular components.

Table 1.

Basic parameters of NGC 1512/1510.

NGC 1512 possesses a unique combination of location, morphological features and environmental characteristics, which makes it an ideal candidate for unravelling the role played by various evolutionary mechanisms in the local Universe. The presence of a bar in NGC 1512 introduces unique dynamics that profoundly impact the galaxy’s structure and evolution, while the close proximity of the galaxy pair offers a unique opportunity to investigate the local impact of the interaction. Limited attention has been given to understanding how the presence of a galactic bar and the interactions with neighbouring galaxies contribute to the evolution of NGC 1512 (Hawarden et al. 1979; Kinman 1978; Li et al. 2008; Koribalski & López-Sánchez 2009; Ma et al. 2017; Smirnova et al. 2020). GALEX (Martin et al. 2005) has observed the galaxy pair NGC 1512/1510 with a resolution of 5″. However, the UltraViolet Imaging Telescope (UVIT) on board AstroSat (Kumar et al. 2012) provides data of higher resolution (of 1.4″). We therefore aim to leverage the high-resolution UV data obtained with UVIT, along with H I data from MeerKAT (Jonas & MeerKAT Team 2016; Jonas 2018), to gain insights into the evolution of NGC 1512.

This study investigates the effects of interaction events and the galactic bar on the evolution of NGC 1512, with the aim being to understand how each of these factors influences star formation activity and galactic morphology. The paper is arranged as follows. The data and analysis are discussed in Sect. 2. Our results and a discussion are presented in Sect. 3, and a summary is given in Sect. 4. We have adopted a flat Universe cosmology throughout this paper with H0 = 71 km s−1 Mpc−1 and ΩM = 0.27 (Komatsu et al. 2011). In the galaxy rest frame, 1″ corresponds to a distance of 60.9 pc.

2. Data and analysis

2.1. UVIT data

To understand the driving mechanisms behind the evolution of the interacting galaxy pair NGC 1512/1510, we use data from UVIT, which are available at the AstroSat ISSDC archive1. UVIT has three bands: Far-UltraViolet (FUV; 130−180 nm), Near-UltraViolet (NUV; 200−300 nm), and VISible (VIS; 320−550 nm), and has the capability to observe simultaneously in all three bands. The VIS channel is used to track the drift of the satellite during observations. The instrument has a 28′ field of view, a spatial resolution of ∼1.4″ and 1.2″ for FUV and NUV filters, respectively, and a plate scale of ∼0.416″ pixel−1. The UVIT therefore provides a better spatial resolution in UV when compared to its predecessor, GALEX.

UVIT observed the galaxy pair NGC 1512/1510 in FUV and NUV channels (PI: K. Saha, Obs. ID: G07_068). NGC 1512 was observed in broadband filters of F154W (FUV, hereafter) and N242W (NUV, hereafter). The observation details are presented in Table 2. We used the software package CCDLab (Postma & Leahy 2017) to reduce the Level 1 data. Drift correction was accounted for using the VIS images. Each image is corrected for fixed pattern noise, distortion, and drift, and was flat fielded using CCDLab (Girish et al. 2017; Postma & Leahy 2017). Final deep images were produced by combining the corrected images. The astrometric solutions were also made using the same software. Figure 1 represents the UVIT colour-composite image of the NGC 1512/1510 pair generated using the emission in FUV and NUV. The zero point magnitude values for the FUV and NUV filters are 17.77 and 19.76 mag, respectively (Tandon et al. 2017, 2020). The inset shows the IRAC 3.6 μm image of the galaxy pair, where the galactic bar in NGC 1512 is visible.

thumbnail Fig. 1.

UVIT colour-composite image of the galaxy pair NGC 1512/1510. The galaxy in the centre is NGC 1512, as indicated by the red cross. The satellite galaxy, NGC 1510, is identified by the red circle and is at a distance of ∼5″ (18.3 kpc) from NGC 1512. The emission in F154W and N242W is represented by blue and yellow colours, respectively. The yellow points in the image are foreground stars, confirmed using the Gaia DR3 catalogue (Gaia Collaboration 2023). The inset shows the IRAC 3.6 μm image of the galaxy, with the galactic bar visible.

Table 2.

Log of observations.

2.2. MeerKAT data

Neutral hydrogen gas (H I) is a good tracer of the gas distribution and kinematics in a galaxy. Previous H I observations of nearby galaxies allowed investigations of the possible triggering mechanisms of starbursts (Lelli et al. 2014; Zhang et al. 2020). We obtained MeerKAT (Jonas & MeerKAT Team 2016; Jonas 2018) L-band raw data from the archive2 (Obs. ID: 20190515-0022) for NGC 1512/1510. The log of observations for the galaxy pair is provided in Table 2. At a frequency of 1.4 GHz, the telescope has a large field of view of 0.85 deg2, covering the galaxy pair. The source J0408−6545 was employed as the flux density or primary calibrator, while the source J0440−4333 was the gain calibrator. We carried out data reduction using CARACal (Józsa et al. 2020), which included both continuum and line imaging. We followed the standard data-reduction procedure by removing bad channels, automatic removal of radio frequency interference (RFI; Offringa et al. 2012), and carrying out flux, bandpass, and gain calibration. We used the SoFiA-2 (Serra et al. 2015) tool for detecting H I sources and generating the clean mask used in WSClean (Offringa et al. 2014) cube imaging. Further details on the data calibration, imaging, and source finding are summarised in Healy et al. (2021). In this paper, we only use MeerKAT data to correlate the distribution of H I with the UV distribution for the galaxy pair. A detailed analysis to understand the H I dynamics in the galaxy pair is in preparation.

2.3. Extinction

One of the major drawbacks of studying star formation in the UV continuum is its sensitivity to extinction (Kennicutt 1998). The UV flux determined should therefore be corrected for extinction. We take the rest-frame extinction into account for our studies. The reddening coefficients, c(Hβ)internal, is defined as the ratio of the observed flux density of Hβ to the unreddened flux density of the same line. This gives us an estimation of reddening caused by the interstellar dust. We cross-matched the star-forming regions identified in López-Sánchez et al. (2015) with the identified star-forming regions in this study for reddening coefficient values. In case of a direct match, we adopted the reddening coefficient values for the identified region. For the regions identified for the first time in the present study, we assumed an average value of the reddening coefficient of the five nearest regions identified in the previous study. We estimated the extinction in FUV using the extinction value of Av = 0.029 reported by Schlafly & Finkbeiner (2011) for NGC 1512 and NGC 1510. The total reddening is calculated by taking the sum of rest-frame and Milky Way reddening values, as discussed in Karthick et al. (2014):

E ( B − V ) Total = E ( B − V ) MW + 0.692 × c ( H β ) internal . $$ \begin{aligned} E(B-V)_{\rm Total} = E(B-V)_{\rm MW} + 0.692 \times c(\mathrm{H}\beta )_{\rm internal}. \end{aligned} $$(1)

We used the Cardelli et al. (1989) extinction law with Rv = (AV)/E(B − V) = 3.1 and used the extinction module in Astropy (Astropy Collaboration 2013) to estimate the value of the extinction coefficients (Rλ) for filters of FUV and NUV bands for individual regions. After estimating the total extinction value, we corrected the FUV and NUV magnitudes, which were then used in the subsequent analysis.

2.4. Identification of star-forming regions in NGC 1512

Star-forming regions provide important information about the evolutionary sequence of a galaxy. We made use of the ProFound package to identify the brightest regions from the UVIT FUV band images. ProFound is an astronomical data-processing tool available in the R programming language (Robotham et al. 2018). Using watershed deblending, ProFound locates the image’s peak flux areas and identifies the source segments. The total photometry is then estimated using iterative expansion (dilation) of the observed segments. Considering the spatial resolution of the UVIT FUV filter (∼1.4″; Borgohain et al. 2022), we defined a criterion that the identified regions should cover at least six pixels (the minimum number of pixels to cover a circle with a diameter equal to the spatial resolution of the FUV filter. A skycut of 3 was applied to identify star-forming regions. Details on source identification and background estimation are found in Robotham et al. (2018) and Ujjwal et al. (2022). We identified 241 bright regions in the UVIT FUV image associated with the main galaxy NGC 1512.

2.5. Identification of spiral arms in NGC 1512

We observe the presence of a bright nuclear region and an inner ring in NGC 1512. We try to understand the morphology of the spiral arms in the galaxy. Previous studies of NGC 1512 noted a single spiral arm beginning at the northeast edge of the inner ring and wrapping continuously around NGC 1512 for an azimuthal angle of nearly 540° (Thilker et al. 2007; Bresolin et al. 2012).

To understand and segregate the identified regions into different arms, we estimated the deprojected distance of the regions along the line of sight using the Eqs. (1)–(11) provided in Sect. 2 of van der Marel & Cioni (2001). We observed that the regions arching from the NE of the inner ring of the main galaxy towards the satellite galaxy appear closer along the line of sight compared to the regions in the SW of the inner ring and in the immediate vicinity of the satellite galaxy. The estimated distance difference between the regions originating from NE of the inner ring and those originating from SW of the inner ring is of the order of ∼20 kpc. The MeerKAT H I image of the galaxy also shows a similar trend. The regions originating from the NE of the inner ring have a continuous gas distribution and wind around the galaxy, while the regions in the SW of the inner ring and near the satellite galaxy exhibit a distorted H I distribution that extends outwards, as is visible in Fig. 2 (left panel).

thumbnail Fig. 2.

H I distribution and morphology of NGC 1512. Left: FUV image of NGC 1512 overplotted with MeerKAT H I column density contours. The contours of red, magenta, blue, and green colours represent column-density values (0.3, 0.35, 0.4 and 0.45) × 1021 cm−2 respectively. We extracted the contour over the galactic bar from the IRAC 3.6 μm image to identify its extent and overplotted it in yellow on the FUV image. Right: a schematic diagram of the morphologies identified in NGC 1512. The blue dotted line represents Arm 1, the orange dash-dotted line represents Arm 2, and the green continuous line represents the inner ring. The galaxy centres for NGC 1512 and NGC 1510 are represented with a cross and an open circle, respectively.

Keeping this distribution in mind, we identify the spiral arms of the galaxy as follows. Arm 1 originates from NE of the inner ring and traces the galaxy for 540° azimuthally and Arm 2 originates from the SW region of the inner ring (Fig. 2, right panel). Arm 2 undergoes disruption due to the interaction between the galaxy pair. It also shows a tidal bridge-like feature that extends from the main galaxy towards the satellite galaxy, beyond which it extends outwards. The regions identified as part of Arm 1 are represented with a dotted line, whereas Arm 2 is represented with a dash-dotted line in Fig. 2. We also detect the galactic bar in NGC 1512 using the IRAC 3.6 μm image (PI: R. Kennicutt). The identified bar region is shown in yellow in the left panel of Fig. 2. The half-length of the bar is measured to be ∼73.5″ (4.4 ± 0.33 kpc) using the analysis of Peters & Kuzio de Naray (2018). Compared to the previous studies, UVIT allows us to study the star-forming regions individually and therefore to study the possible effect of interaction in detail.

3. Results and discussion

3.1. Estimation of SFR

The ProFound module provides the number of pixels containing 100% of the flux for all of the 241 identified regions. We used this to calculate the area of each region and also obtain the counts from the same using ProFound. The counts in the selected regions were integration-time-weighted and converted to magnitude units using the zero point conversion factor, as discussed in Tandon et al. (2020). We corrected for extinction in the obtained magnitudes, in accordance with Sect. 2.3. We removed star-forming regions with dereddened FUV magnitude, mFUV, fainter than 21 mag in order to exclude regions with photometric errors larger than 0.1 mag (Devaraj et al. 2023). We obtained a final sample of 175 star-forming regions in NGC 1512. We note that with the exception of the analysis in Sect. 3.4, the regions of NGC 1510 have not been considered. The corresponding SFRs were then calculated using Eq. (4) in Karachentsev & Kaisina (2013), as follows:

log ( SFR [ M ⊙ yr − 1 ] ) = 2.78 − 0.4 × m FUV c + 2 × log D , $$ \begin{aligned} \log (\mathrm{SFR}[M_{\odot }\,\mathrm{yr}^{-1}]) = 2.78 - 0.4 \times m^\mathrm{c}_{\rm FUV} + 2 \times \log D, \end{aligned} $$(2)

where m FUV c $ {m^{\mathrm{c}}_{\mathrm{FUV}}} $ denotes the total extinction-corrected FUV magnitude, and D is the distance to the galaxy in megaparsecs. The error in counts was estimated using Poisson’s distribution. The errors associated with m FUV c $ {m^{\mathrm{c}}_{\mathrm{FUV}}} $ and SFR were obtained from error propagation (Bevington & Robinson 1992).

To understand the effects of different galactic properties on determination of the SFR and the propagation of star formation throughout the galaxy, we classified the regions according to their positions in the galaxy. We made use of the values of distance, the coordinates for the centre of the main galaxy, inclination, and position angle for the galaxy from Table 1 and employed the analysis carried out by van der Marel & Cioni (2001) to estimate galactocentric distance in kiloparsecs for each identified region.

We estimated the star formation rate densities (SFRDs) of identified regions by dividing the estimated SFRs by the area of each region (in kpc2). Figure 3 (left panel) is a radial distribution of the logarithmic values of SFRD for the identified regions from the centre of the galaxy. We demarcated different regions of the galaxy as A, B, and C on the basis of Fig. 2 (right panel) to understand the trends in the spatial distribution of SFRD. A denotes the star-forming regions identified in the nuclear region of the galaxy (represented as green triangles), A spans a radial distance of ∼10″ (∼0.6 kpc) from the centre of NGC 1512. B denotes the regions in the inner ring (represented as brown inverted triangles). B excludes the star-forming regions from A and spans a distance from ∼10″ to 115″ (∼0.6−7 kpc). C denotes the regions identified as part of the spiral arms. The blue circles denote regions identified as part of Arm 1, and the red squares denote regions identified as part of Arm 2. We note that the nuclear region of the galaxy (A) exhibits heightened rates of star formation. We also observed higher values of SFRD in the inner ring region (B). This shows enhanced star formation occurring in the nuclear region, the circumnuclear ring, and the inner ring of the galaxy. As we move radially outwards, the SFRD decreases along the spiral arm regions (C), which aligns with the expected distribution of star formation in a typical spiral galaxy (Martel et al. 2013). However, some regions, for example those at radial distances of 12 kpc and 30 kpc, show small peaks in the SFRD distribution, as is presented in Fig. 3 (left panel). These localised enhancements in star formation present an interesting radial profile, suggesting the presence of additional factors influencing star-formation dynamics in specific regions.

thumbnail Fig. 3.

Distribution of SFRD in NGC 1512. Left: distribution of SFRD of the regions with respect to the deprojected radial distance from the centre of the galaxy. The SFRD of a region is calculated by dividing its estimated SFR by the area of the region in kpc2. It can be observed that the nuclear and inner ring regions of the galaxy (Areas A and B) exhibit higher orders of SFRD (log(SFRD[M⊙ yr−1 kpc−2]) > −1.5). On the other hand, the regions of the spiral exhibit lower SFRD (Area C). The histograms parallel to the axes show the distribution of the SFRD and the distance from the centre of NGC 1512 for the corresponding regions. Right: the regions identified as part of Arms 1 and 2. The circular symbols represent Arm 1, while the diamond symbols represent Arm 2. The trajectories of the spiral arms, as identified in Fig. 2 (right panel), are plotted to indicate their positions. We see an asymmetric distribution of SFRDs. Region I coincides with the origin of Arm 1 and exhibits enhanced star formation (log(SFRDmean[M⊙ yr−1 kpc−2]) ∼ −2.01). Region II shows local enhancements of star formation, with (log(SFRDmean[M⊙ yr−1 kpc−2]) ∼ −2.28). Regions in the outer part of Arm 1, denoted by Region III, also show heightened values when compared to other regions of Arm 1, with log(SFRDmean[M⊙ yr−1 kpc−2]) ∼ −2.36.

The observed phenomena in the radial distribution of the identified regions can be better understood by studying the local trends in the star-formation properties. Our study of the identified regions in the arms of the galaxy is presented in Sect. 3.2 and our study of the inner ring is shown in Sect. 3.3.

3.2. Studying the star formation properties along the spiral arms

The formation scenario of spiral structures in galaxies has been attributed to different factors that can be secular or environmental in nature. Environmental effects due to interaction, such as tidal effects, may instigate a spiral structure due to the presence of a massive or satellite companion or may create distortions in the already existing structures (Toomre & Toomre 1972; Donner et al. 1991; Struck et al. 2011). Therefore, studying the spiral arms of the galaxy will help us to understand the role of interactions in shaping the spiral arms of the galaxy. In this context, we study star formation along the spiral arms of NGC 1512. We intend to comprehend and compare the properties of Arms 1 and 2, which are defined in Sect. 3. This will help us to understand the effect of the interaction between the main galaxy and the satellite galaxy. To compare the physical properties of Arms 1 and 2, we performed a two-sample Kolmogorov–Smirnov test (K-S test; Pratt & Gibbons 1981) on the properties of the star-forming regions to check whether the properties of Arms 1 and 2 are significantly different or not. When the K-S test is performed for the SFRD of the star-forming regions, the p-value is 0.27, suggesting that the regions may have similar star formation properties. When the test is carried out in order to assess the distribution of the area of the identified regions, the p-value is 0.04. Therefore, from the K-S test, we note that there may not be significant differences in the overall star formation properties of the identified star-forming regions in the arms. We therefore looked for localised effects of the interaction event on the two spiral arms.

The interaction episode of NGC 1512 with NGC 1510 has created disruptions in the spiral arms. The interaction has resulted in disruptions to the regions originating from the SW of the inner ring, which have formed a tidal bridge towards the satellite galaxy. Furthermore, Arm 1 has undergone visible distortions due to interaction, as is visible in Fig. 2 (left panel). These observations provide valuable insights into the complex interplay between galaxy interactions and the morphology of spiral galaxies. The distortions observed in the spiral arms of NGC 1512 highlight the effects that interaction events can have on the intricate structure of a galaxy.

In Fig. 3 (right panel), we plot the regions identified in the spiral arms of the galaxy, Arms 1 and 2. The regions are colour-coded based on the intensity of the calculated SFRD. We observe three regions in the arms exhibiting higher SFRD values compared to the other regions in the arms (log(SFRD[M⊙ yr−1 kpc−2]) > −2.4), which represents the highest 85th percentile in log(SFRD) values. We consider these three regions of interest, labelled I, II, and III in Fig. 3 (right panel). These regions have been named in decreasing order of their SFRD values.

We observed heightened SFRD values at the origin of Arm 1, denoted Region I. The observed enhancement is a possible effect of a combination of orbit crowding, cloud collisions, and gravitational instabilities (Elmegreen 2009; Urquhart et al. 2021). We estimated a mean log(SFRD[M⊙ yr−1 kpc−2]) value of −2.01 ± 0.02 for this region. Numerical simulations were used by Renaud et al. (2013, 2015) to investigate the role of bars in triggering star formation, with the authors concluding that the leading edges of the bars favour converging gas flows and large-scale shocks.

Star-forming regions identified in the region of interaction between the main and satellite galaxy (Region II) exhibit higher SFRD values than other regions associated with Arm 2. This observed enhancement exhibits the important role that the interaction with NGC 1510 plays in shaping the main galaxy. Region II has a mean log(SFRD[M⊙ yr−1 kpc−2]) value of −2.28 ± 0.03 in comparison to the mean log(SFRD[M⊙ yr−1 kpc−2]) value of −2.67 ± 0.04 for star-forming regions in Arm 2, excluding Region II. This means that the interaction event of NGC 1512 with NGC 1510 has not only disrupted Arm 2 but may also have triggered local bursts of star formation in the vicinity of the interaction. This region is embedded in a high-density region in the H I column density map (refer to Fig. 2, left panel), which shows that the interaction event has created a zone of intense star formation in the region of interaction. We also observe that the H I has a non-uniform distribution in this region. The observed enhancements in star formation and H I column density are possibly the result of the interaction event between the galaxy pair (Keel 1991; Struck 1999).

Di Teodoro & Fraternali (2014) proposed a relation to estimate the gas-accretion rate from minor mergers onto star-forming galaxies, which is given as:

M ˙ H i = ∑ i = 0 n M H i , i / T 0 , i , $$ \begin{aligned} \dot{M}_{\mathrm{H}i } = \sum _{{i=0}}^{{n}} {M}_{\mathrm{H}i ,i}/T_{{0,i}}, \end{aligned} $$(3)

where ṀH I is the mass-accretion rate, MH I,i denotes the H I mass of the ith dwarf galaxy, and T0, i is the dynamical time taken for the completion of the minor merger events of i dwarf companions with the massive galaxy. For our case, we consider the case of the dwarf galaxy NGC 1510 as a satellite. As the galaxy pairs are already extremely close to each other (∼18.3 kpc) and H I envelopes are already interacting, we assume that the minor merger will be completed in a dynamical time of about 1 Gyr. We estimated the H I mass of NGC 1510 as 2.84 × 107 M⊙ (Barnes et al. 2001). By substituting the values, we estimate the mass-accretion rate of H I gas from the satellite galaxy to be around 2 × 10−2 M⊙ yr−1. The estimated accretion rate is one-fifth of the global SFR of NGC 1512 estimated in the present study (∼0.11 M⊙ yr−1). This suggests that the ongoing accretion event might not be the major driver of the star formation in NGC 1512 (Di Teodoro & Fraternali 2014). Further analysis might help us to understand the other factors influencing star formation in the main galaxy.

Region III belongs to the outer regions of Arm 1. We observe high SFRD values (mean log(SFRD[M⊙ yr−1 kpc−2]) value ∼ − 2.36 ± 0.04) in this region. These regions also exhibit a higher H I column density compared to other regions identified in the outskirts of Arm 1. These are indicators of ongoing star formation. It is possible that the enhancement in SFRD and the higher H I observed in Region III are due to previous interaction events or minor mergers that the main galaxy might have undergone over the last few gigayears. When a galaxy falls into a larger host galaxy, it can bring gas that fuels star formation in the outskirts of the host galaxy (Malin & Hadley 1997). In the past, these remnants from merger events became more diffuse and indistinguishable from the other regions of the galaxy (Martínez-Delgado et al. 2009, 2010). Therefore, we realise that past interactions of NGC 1512 are a possible reason for the observed morphology of spiral arms and local enhancements of star formation on the outskirts of the spiral arms.

Based on the observations of localised enhancements of SFRD and higher H I column density in NGC 1512, we suggest that past and ongoing interaction events may have instigated local bursts of star formation and contributed to the shaping of the galaxy. The enhanced SFRD and higher H I column density observed in these regions are potentially the result of interaction episodes: with the satellite galaxy NGC 1510 in Region II and older interaction episodes in the outskirts of Arm 1. Our observations show a positive correlation between the regions exhibiting higher H I column density and enhancements in SFRD. Therefore, the observed enhancement in star formation and the morphology of the spiral arms in NGC 1512 suggest that interaction events have played a significant role in the evolutionary history of the galaxy. The effects of these interactions may have been long-lasting, with the remnants of past mergers and interactions becoming more diffuse over time and integrated into the overall structure of the galaxy.

3.3. Star formation in the inner ring

While the interaction with its satellite galaxy has had significant effects on both the morphology and star formation properties of NGC 1512, the presence of a strong bar in the galaxy (bar strength of Qb ∼ 0.27; Buta et al. 2005, 2006) can influence its evolution. Schwarz (1981, 1984) discussed the formation of rings in a galaxy as a result of its secular evolution due to bar-driven gas flow. The presence of a bar can funnel the cold gas inside the co-rotation radius to the nuclear region, leading to a dearth of cold gas in the co-rotation radius region (Haywood et al. 2016; George et al. 2019, 2020).

Previous studies have been unable to resolve the star-forming regions in the inner ring of NGC 1512. However, owing to the superior resolving power of UVIT, we have been able to resolve individual star-forming regions, allowing us to study the properties of the regions in detail. The inner ring holds the promise of new discoveries, as it encircles the bar at 3′ from the galactic centre and has been largely unexplored. The main goal of this analysis is to study the physical properties of the identified regions in the inner ring in order to better understand the effect of the galactic bar on the inner ring.

We observed a concentration of star-forming regions in the inner ring region near the major axis of the bar, as is visible in Fig. 2 (left panel). We note from Fig. 3 (left panel) that the inner ring shows the highest values for SFRD (log(SFRDmean[M⊙ yr−1 kpc−2]) ∼ −1.7). The driving force behind these heightened values of the SFRD needs to be understood. We used the deprojected coordinate values for each region such that the major axis of the galaxy coincides with the X-axis. We then estimated the angle subtended by each region with respect to north in the counter-clockwise direction, with 0° denoting the positive Y-axis. Figure 4 represents the distribution of SFRD along the angle subtended by the regions with the inner ring of the galaxy. We observe in Fig. 4 that the regions lying in the region of the conjunction between the end of the bar and the inner ring, near 45° and 225°, show heightened star formation. There is a clustering of star-forming regions around the major axis of the bar that show heightened star formation activity.

thumbnail Fig. 4.

Distribution of SFRD in the identified regions of the inner ring of the galaxy (region shown in the inset of Fig. 1) based on their angles relative to north in a boxplot. The box represents the interquartile range of the observed SFRD, the orange stars indicate the median of the SFRD, and the whiskers depict data points within the range of 1.5 times the interquartile range. Outliers, depicted as green diamonds beyond the whisker limits, are values that fall outside this range. Individual hyphen markers in some places indicate that only a single star-forming region subtends the corresponding angle. We observe a peak in the SFRD at the area of the inner ring in conjunction with the ends of the bar.

The formation of an inner ring in galaxies has been attributed to gas being caught at the ultraharmonic resonance (UHR) position of the galaxy, preventing it from being funnelled by the bar towards the galactic centre (Schwarz 1984; Lord & Kenney 1991; Buta et al. 2004; Byrd et al. 2006). We understand that due to further compression and shocks in the trapped gas, leading to a possible crowding effect, star formation can be enhanced in this region. This is supported by the observed trends in SFRD for the inner ring, with heightened star formation activity around the major axis of the bar.

We studied the star formation activity inside the region of the bar (as identified in the left panel of Fig. 2) of the galaxy and found a distinct lack of UV emission in this region. This suggests that there is no ongoing or recent star formation occurring in this region. To further understand the possible reason behind the absence of star formation inside the bar region, we overlaid the H I column density over the UVIT image in Fig. 2 (left panel). Our analysis shows a lack of H I distribution in this region when compared to the surrounding regions. Such a distribution hints at a possible variation in the distribution of neutral hydrogen gas and a potential deviation from typical gas dynamics in the observed region. This indicates that the H I gas in the galaxy is being redistributed, and its distribution inside the bar region is affected by the presence of the galactic bar (e.g. George et al. 2019, 2020; Saha et al. 2021). The identified region also lacks CO(2−1) gas (Lee et al. 2023). These observations highlight the importance of galactic bars on star formation and H I gas distribution in galaxies. It is crucial to understand how the presence of galactic bars affects the evolution of galaxies and how this contributes to the overall distribution of H I gas and star formation in a galaxy.

Based on our analysis, it can be inferred that the galactic bar plays a significant role in driving the secular evolution of NGC 1512. This is in addition to the effects of past and ongoing interaction events that may also be contributing to the observed properties of the galaxy. We find that the galactic bar plays a critical role in redistributing H I gas in the inner regions of the galaxy and in the subsequent quenching of star formation inside the bar radius. The redistribution of the H I gas in the central regions of the galaxy is likely driven by the non-axisymmetric gravitational potential created by the bar. This is the first study designed to improve our understanding of the combined effects of the galactic bar and the interaction with the satellite galaxy on the evolution of NGC 1512.

Our findings demonstrate that a combination of secular and environmental factors influences the evolution of NGC 1512. The interplay between these effects shapes the observed properties and evolution of NGC 1512.

3.4. Star formation in the satellite galaxy NGC 1510

The satellite galaxy NGC 1510 is classified as a blue compact dwarf (BCD) galaxy and is situated at a distance of ∼5′ (∼18.3 kpc) from NGC 1512. We observed the satellite galaxy to be embedded in a region that is highly dense in H I gas (> 0.45 × 1021 cm−2). We identified three star-forming regions in the galaxy with values of log(SFRD[M⊙ yr−1 kpc−2]) ranging from −0.71 to −2.65. We conclude that the satellite galaxy is experiencing enhanced levels of star formation. Hawarden et al. (1979) suggested the observed blue colour of the satellite galaxy was a result of the high H I column density region it contains. The observed region of high H I column density in which the satellite galaxy is embedded may be due to gas capture by the satellite galaxy from the main galaxy (Hawarden et al. 1979; Gallagher et al. 2005).

4. Summary

We conducted this study to investigate the impact of interaction events and the galactic bar on the evolution of the interacting galaxy pair NGC 1512/1510. The aim of this study is to provide insight into the factors driving the observed morphological and star-forming properties of NGC 1512 and to elucidate the mechanisms that govern galactic evolution in the context of interaction and secular processes. A summary of the main results obtained from our study is given below.

  • We used the UVIT FUV and NUV observations to identify and characterise the star-forming regions in the galaxy pair.

  • We identified 175 star-forming regions in the UVIT FUV image of NGC 1512 using the ProFound package. The calculated magnitudes were extinction corrected.

  • We identified regions that exhibit enhanced SFRD. We observe that in addition to the enhancement of star formation near the origin of Arm 1, enhancement is observed in the region of interaction between the galaxy pair and on the outskirts of Arm 1. These star-forming regions have high H I density.

  • The observed enhancements in SFRD and H I density in the interaction regions between the galaxy pair and the outskirts of Arm 1 indicate that the evolution of NGC 1512 is intimately linked to its interaction history.

  • We observed heightened star formation activity in the inner ring near the ends of the galactic bar. The conspicuous lack of both UV and H I emission detected within the bar radius points towards the redistribution of gas in the central regions of the galaxy. This action is seen to force the gas to migrate inwards towards the central regions of the galaxy, causing a depletion of gas supply and eventually suppression of star formation activity.

  • Our study finds enhanced star formation in NGC 1510. This is consistent with the region of high H I column density (> 0.45 × 1021 cm−2) within the galaxy.

We conclude that the galaxy NGC 1512 owes its present state to different evolutionary factors, both environmental and secular. To further quantify the effect of each of these factors in galactic evolution, numerical simulations will be crucial. These simulations can help us to understand the details of the gas dynamics and star formation history of the galaxy and provide more insight into how each factor has influenced the evolution of NGC 1512.

Acknowledgments

We thank the anonymous referee for the valuable comments and suggestions that have improved the quality of the paper. We acknowledge the financial support from the Indian Space Research Organisation (ISRO) under the AstroSat archival data utilisation program (No. DS-2B-13013(2)/6/2019) and the Department of Science and Technology (DST) for the INSPIRE FELLOWSHIP (IF180855). We thank our colleagues Shridharan Baskaran, Akhil Krishna R, Cysil Tom Baby and Belinda Damian for their valuable comments on the manuscript. This publication uses the data from the UVIT, which is part of the AstroSat mission of the ISRO, archived at the Indian Space Science Data Centre (ISSDC). We gratefully thank all the individuals involved in the various teams for supporting the project from the early stages of the design to launch and observations with it in orbit. We thank Joseph Postma, University of Calgary, for his consistent support during the process of UVIT data reduction. We thank the Center for Research, CHRIST (Deemed to be University), for all their support during the course of this work. This research has used the NASA/IPAC Extragalactic Database (NED), funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

References

  1. Astropy Collaboration (Robitaille, T. P., et al.) 2013, A&A, 558, A33 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
  2. Barnes, D. G., Staveley-Smith, L., de Blok, W. J. G., et al. 2001, MNRAS, 322, 486 [Google Scholar]
  3. Bevington, P. R., & Robinson, D. K. 1992, Data Reduction and Error Analysis for the Physical Sciences (Boston: McGraw-Hill) [Google Scholar]
  4. Borgohain, A., Saha, K., Elmegreen, B., et al. 2022, Nature, 607, 459 [NASA ADS] [CrossRef] [Google Scholar]
  5. Bresolin, F., Kennicutt, R. C., & Ryan-Weber, E. 2012, ApJ, 750, 122 [NASA ADS] [CrossRef] [Google Scholar]
  6. Buta, R. J., Byrd, G. G., & Freeman, T. 2004, AJ, 127, 1982 [NASA ADS] [CrossRef] [Google Scholar]
  7. Buta, R., Vasylyev, S., Salo, H., & Laurikainen, E. 2005, AJ, 130, 506 [NASA ADS] [CrossRef] [Google Scholar]
  8. Buta, R., Laurikainen, E., Salo, H., Block, D. L., & Knapen, J. H. 2006, AJ, 132, 1859 [NASA ADS] [CrossRef] [Google Scholar]
  9. Byrd, G. G., Freeman, T., & Buta, R. J. 2006, AJ, 131, 1377 [NASA ADS] [CrossRef] [Google Scholar]
  10. Cardelli, J. A., Clayton, G. C., & Mathis, J. S. 1989, ApJ, 345, 245 [Google Scholar]
  11. Chakrabarti, S., Bigiel, F., Chang, P., & Blitz, L. 2011, ApJ, 743, 35 [NASA ADS] [CrossRef] [Google Scholar]
  12. de Vaucouleurs, G., de Vaucouleurs, A., Corwin, H. G., Jr., et al. 1991, Third Reference Catalogue of Bright Galaxies (New York: Springer) [Google Scholar]
  13. Devaraj, A., Joseph, P., Stalin, C. S., Tandon, S. N., & Ghosh, S. K. 2023, ApJ, 946, 65 [NASA ADS] [CrossRef] [Google Scholar]
  14. Di Teodoro, E. M., & Fraternali, F. 2014, A&A, 567, A68 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
  15. Donner, K. J., Engstrom, S., & Sundelius, B. 1991, A&A, 252, 571 [NASA ADS] [Google Scholar]
  16. Doyle, M. T., & Drinkwater, M. J. 2006, MNRAS, 372, 977 [Google Scholar]
  17. Ducci, L., Kavanagh, P. J., Sasaki, M., & Koribalski, B. S. 2014, A&A, 566, A115 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
  18. Elmegreen, B. G. 2009, in The Galaxy Disk in Cosmological Context, eds. J. Andersen, B. M. Nordströara, & J. Bland-Hawthorn, 254, 289 [NASA ADS] [Google Scholar]
  19. Gaia Collaboration (Vallenari, A., et al.) 2023, A&A, 674, A1 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
  20. Gallagher, J. S., Grebel, E. K., Smith, L. J., & Jerjen, H. 2005, IAU Colloq., 198, 151 [CrossRef] [Google Scholar]
  21. George, K., Joseph, P., Mondal, C., et al. 2019, A&A, 621, L4 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
  22. George, K., Joseph, P., Mondal, C., et al. 2020, A&A, 644, A79 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
  23. Girish, V., Tandon, S. N., Sriram, S., Kumar, A., & Postma, J. 2017, Exp. Astron., 43, 59 [NASA ADS] [CrossRef] [Google Scholar]
  24. Hawarden, T. G., van Woerden, H., Mebold, U., Goss, W. M., & Peterson, B. A. 1979, A&A, 76, 230 [NASA ADS] [Google Scholar]
  25. Haywood, M., Lehnert, M. D., Di Matteo, P., et al. 2016, A&A, 589, A66 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
  26. Healy, J., Deb, T., Verheijen, M. A. W., et al. 2021, A&A, 654, A173 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
  27. Jonas, J. 2018, Proceedings of MeerKAT Science: On the Pathway to the SKA, 277 [Google Scholar]
  28. Jonas, J., & MeerKAT Team 2016, Proceedings of MeerKAT Science: On the Pathway to the SKA, 1 [Google Scholar]
  29. Józsa, G. I. G., White, S. V., Thorat, K., et al. 2020, ASP Conf. Ser., 527, 635 [Google Scholar]
  30. Karachentsev, I. D., & Kaisina, E. I. 2013, AJ, 146, 46 [NASA ADS] [CrossRef] [Google Scholar]
  31. Karthick, M. C., López-Sánchez, Á. R., Sahu, D. K., Sanwal, B. B., & Bisht, S. 2014, MNRAS, 439, 157 [NASA ADS] [CrossRef] [Google Scholar]
  32. Keel, W. C. 1991, IAU Symp., 146, 243 [NASA ADS] [Google Scholar]
  33. Kennicutt, R. C., Jr. 1998, ARA&A, 36, 189 [Google Scholar]
  34. Kennicutt, R. C., & Evans, N. J. 2012, ARA&A, 50, 531 [NASA ADS] [CrossRef] [Google Scholar]
  35. Kinman, T. D. 1978, AJ, 83, 764 [NASA ADS] [CrossRef] [Google Scholar]
  36. Komatsu, E., Smith, K. M., Dunkley, J., et al. 2011, ApJS, 192, 18 [Google Scholar]
  37. Koribalski, B. S., & López-Sánchez, Á. R. 2009, MNRAS, 400, 1749 [NASA ADS] [CrossRef] [Google Scholar]
  38. Koribalski, B. S., Staveley-Smith, L., Kilborn, V. A., et al. 2004, AJ, 128, 16 [Google Scholar]
  39. Kormendy, J., & Kennicutt, R. C., Jr. 2004, ARA&A, 42, 603 [Google Scholar]
  40. Kumar, A., Ghosh, S. K., Hutchings, J., et al. 2012, Proc. SPIE, 8443, 84431N [NASA ADS] [CrossRef] [Google Scholar]
  41. Lee, J. C., Sandstrom, K. M., Leroy, A. K., et al. 2023, ApJ, 944, L17 [NASA ADS] [CrossRef] [Google Scholar]
  42. Lelli, F., Verheijen, M., & Fraternali, F. 2014, MNRAS, 445, 1694 [Google Scholar]
  43. Leroy, A. K., Walter, F., Brinks, E., et al. 2008, AJ, 136, 2782 [Google Scholar]
  44. Li, C., Kauffmann, G., Heckman, T. M., White, S. D. M., & Jing, Y. P. 2008, MNRAS, 385, 1915 [CrossRef] [Google Scholar]
  45. Lord, S. D., & Kenney, J. D. P. 1991, ApJ, 381, 130 [NASA ADS] [CrossRef] [Google Scholar]
  46. López-Sánchez, A. R., Westmeier, T., Esteban, C., & Koribalski, B. S. 2015, MNRAS, 450, 3381 [CrossRef] [Google Scholar]
  47. Ma, C., de Grijs, R., & Ho, L. C. 2017, ApJS, 230, 14 [NASA ADS] [CrossRef] [Google Scholar]
  48. Maeda, F., Egusa, F., Ohta, K., Fujimoto, Y., & Habe, A. 2023, ApJ, 943, 7 [NASA ADS] [CrossRef] [Google Scholar]
  49. Malin, D., & Hadley, B. 1997, PASA, 14, 52 [NASA ADS] [CrossRef] [Google Scholar]
  50. Maoz, D., Barth, A. J., Ho, L. C., Sternberg, A., & Filippenko, A. V. 2001, AJ, 121, 3048 [NASA ADS] [CrossRef] [Google Scholar]
  51. Martel, H., Kawata, D., & Ellison, S. L. 2013, MNRAS, 431, 2560 [Google Scholar]
  52. Martin, D. C., Fanson, J., Schiminovich, D., et al. 2005, ApJ, 619, L1 [Google Scholar]
  53. Martínez-Delgado, D., Pohlen, M., Gabany, R. J., et al. 2009, ApJ, 692, 955 [CrossRef] [Google Scholar]
  54. Martínez-Delgado, D., Gabany, R. J., Crawford, K., et al. 2010, AJ, 140, 962 [Google Scholar]
  55. Mathewson, D. S., & Ford, V. L. 1996, ApJS, 107, 97 [Google Scholar]
  56. Meurer, G. R., Hanish, D. J., Ferguson, H. C., et al. 2006, ApJS, 165, 307 [NASA ADS] [CrossRef] [Google Scholar]
  57. Offringa, A. R., van de Gronde, J. J., & Roerdink, J. B. T. M. 2012, A&A, 539, A95 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
  58. Offringa, A. R., McKinley, B., & Hurley-Walker, N. 2014, MNRAS, 444, 606 [NASA ADS] [CrossRef] [Google Scholar]
  59. Parkash, V., Brown, M. J. I., Jarrett, T. H., & Bonne, N. J. 2018, ApJ, 864, 40 [NASA ADS] [CrossRef] [Google Scholar]
  60. Peters, W., & Kuzio de Naray, R. 2018, MNRAS, 476, 2938 [NASA ADS] [CrossRef] [Google Scholar]
  61. Postma, J. E., & Leahy, D. 2017, PASP, 129, 115002 [Google Scholar]
  62. Pratt, J. W., & Gibbons, J. D. 1981, Concepts of Nonparametric Theory (Springer), 318 [CrossRef] [Google Scholar]
  63. Renaud, F., Bournaud, F., Emsellem, E., et al. 2013, MNRAS, 436, 1836 [NASA ADS] [CrossRef] [Google Scholar]
  64. Renaud, F., Bournaud, F., Emsellem, E., et al. 2015, MNRAS, 454, 3299 [NASA ADS] [CrossRef] [Google Scholar]
  65. Robotham, A. S. G., Davies, L. J. M., Driver, S. P., et al. 2018, MNRAS, 476, 3137 [NASA ADS] [CrossRef] [Google Scholar]
  66. Saha, K., Dhiwar, S., Barway, S., Narayan, C., & Tandon, S. 2021, JApA, 42, 59 [NASA ADS] [Google Scholar]
  67. Schlafly, E. F., & Finkbeiner, D. P. 2011, ApJ, 737, 103 [Google Scholar]
  68. Schwarz, M. P. 1981, ApJ, 247, 77 [NASA ADS] [CrossRef] [Google Scholar]
  69. Schwarz, M. P. 1984, MNRAS, 209, 93 [NASA ADS] [CrossRef] [Google Scholar]
  70. Serra, P., Westmeier, T., Giese, N., et al. 2015, MNRAS, 448, 1922 [Google Scholar]
  71. Skibba, R. A., Bamford, S. P., Nichol, R. C., et al. 2009, MNRAS, 399, 966 [NASA ADS] [CrossRef] [Google Scholar]
  72. Smirnova, K. I., Wiebe, D. S., Moiseev, A. V., & Jozsa, G. I. G. 2020, Astrophys. Bull., 75, 234 [NASA ADS] [CrossRef] [Google Scholar]
  73. Struck, C. 1999, Phys. Rep., 321, 1 [NASA ADS] [CrossRef] [Google Scholar]
  74. Struck, C., Dobbs, C. L., & Hwang, J.-S. 2011, MNRAS, 414, 2498 [NASA ADS] [CrossRef] [Google Scholar]
  75. Tandon, S. N., Subramaniam, A., Girish, V., et al. 2017, AJ, 154, 128 [NASA ADS] [CrossRef] [Google Scholar]
  76. Tandon, S. N., Postma, J., Joseph, P., et al. 2020, AJ, 159, 158 [Google Scholar]
  77. Thilker, D. A., Bianchi, L., Meurer, G., et al. 2007, ApJS, 173, 538 [Google Scholar]
  78. Toomre, A., & Toomre, J. 1972, ApJ, 178, 623 [Google Scholar]
  79. Tully, R. B., Courtois, H. M., & Sorce, J. G. 2016, AJ, 152, 50 [Google Scholar]
  80. Ujjwal, K., Kartha, S. S., Subramanian, S., et al. 2022, MNRAS, 516, 2171 [CrossRef] [Google Scholar]
  81. Urquhart, J. S., Figura, C., Cross, J. R., et al. 2021, MNRAS, 500, 3050 [Google Scholar]
  82. van der Marel, R. P., & Cioni, M.-R. L. 2001, AJ, 122, 1807 [Google Scholar]
  83. Zhang, H.-X., Smith, R., Oh, S.-H., et al. 2020, ApJ, 900, 152 [NASA ADS] [CrossRef] [Google Scholar]
  84. Zhou, Z., Wu, H., Zhou, X., & Ma, J. 2018, PASP, 130, 094101 [CrossRef] [Google Scholar]

All Tables

Table 1.

Basic parameters of NGC 1512/1510.

In the text
Table 2.

Log of observations.

In the text

All Figures

thumbnail Fig. 1.

UVIT colour-composite image of the galaxy pair NGC 1512/1510. The galaxy in the centre is NGC 1512, as indicated by the red cross. The satellite galaxy, NGC 1510, is identified by the red circle and is at a distance of ∼5″ (18.3 kpc) from NGC 1512. The emission in F154W and N242W is represented by blue and yellow colours, respectively. The yellow points in the image are foreground stars, confirmed using the Gaia DR3 catalogue (Gaia Collaboration 2023). The inset shows the IRAC 3.6 μm image of the galaxy, with the galactic bar visible.
In the text
thumbnail Fig. 2.

H I distribution and morphology of NGC 1512. Left: FUV image of NGC 1512 overplotted with MeerKAT H I column density contours. The contours of red, magenta, blue, and green colours represent column-density values (0.3, 0.35, 0.4 and 0.45) × 1021 cm−2 respectively. We extracted the contour over the galactic bar from the IRAC 3.6 μm image to identify its extent and overplotted it in yellow on the FUV image. Right: a schematic diagram of the morphologies identified in NGC 1512. The blue dotted line represents Arm 1, the orange dash-dotted line represents Arm 2, and the green continuous line represents the inner ring. The galaxy centres for NGC 1512 and NGC 1510 are represented with a cross and an open circle, respectively.
In the text
thumbnail Fig. 3.

Distribution of SFRD in NGC 1512. Left: distribution of SFRD of the regions with respect to the deprojected radial distance from the centre of the galaxy. The SFRD of a region is calculated by dividing its estimated SFR by the area of the region in kpc2. It can be observed that the nuclear and inner ring regions of the galaxy (Areas A and B) exhibit higher orders of SFRD (log(SFRD[M⊙ yr−1 kpc−2]) > −1.5). On the other hand, the regions of the spiral exhibit lower SFRD (Area C). The histograms parallel to the axes show the distribution of the SFRD and the distance from the centre of NGC 1512 for the corresponding regions. Right: the regions identified as part of Arms 1 and 2. The circular symbols represent Arm 1, while the diamond symbols represent Arm 2. The trajectories of the spiral arms, as identified in Fig. 2 (right panel), are plotted to indicate their positions. We see an asymmetric distribution of SFRDs. Region I coincides with the origin of Arm 1 and exhibits enhanced star formation (log(SFRDmean[M⊙ yr−1 kpc−2]) ∼ −2.01). Region II shows local enhancements of star formation, with (log(SFRDmean[M⊙ yr−1 kpc−2]) ∼ −2.28). Regions in the outer part of Arm 1, denoted by Region III, also show heightened values when compared to other regions of Arm 1, with log(SFRDmean[M⊙ yr−1 kpc−2]) ∼ −2.36.
In the text
thumbnail Fig. 4.

Distribution of SFRD in the identified regions of the inner ring of the galaxy (region shown in the inset of Fig. 1) based on their angles relative to north in a boxplot. The box represents the interquartile range of the observed SFRD, the orange stars indicate the median of the SFRD, and the whiskers depict data points within the range of 1.5 times the interquartile range. Outliers, depicted as green diamonds beyond the whisker limits, are values that fall outside this range. Individual hyphen markers in some places indicate that only a single star-forming region subtends the corresponding angle. We observe a peak in the SFRD at the area of the inner ring in conjunction with the ends of the bar.
In the text

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.