Issue 
A&A
Volume 563, March 2014



Article Number  A27  
Number of page(s)  17  
Section  Extragalactic astronomy  
DOI  https://doi.org/10.1051/00046361/201322658  
Published online  27 February 2014 
Online material
Appendix A: asymmetricdrift correction
To calculate the asymmetricdrift correction, we start from Eq. (433) of Binney & Tremaine (1987), which describes a stationary, axisymmetric stellar system embedded in a gravitational potential Φ(R,z): (A.1)where v_{R}, v_{z}, and v_{φ} are the components (in cylindrical coordinates) of the velocity of a star, ρ is the stellar density, , , , and . The observed stellar rotation curve v_{rot} provides . Note that Eq. (A.1) does not require that the velocity dispersion is smaller than the rotation velocity. Following Weijmans et al. (2008), we write (A.2)where κ = 0 and κ = 1 correspond, respectively, to the extreme cases of a velocity ellipsoid aligned with the cylindrical (R, z, φ) and spherical (r, θ, φ) coordinate systems. Using higherorder velocitymoments of the collisionless Boltzmann equation, Weijmans et al. (2008) obtained the following expressions (see their Appendix A): (A.3)and (A.4)where (A.5)The last term of Eq. (A.3) vanishes if the velocity ellipsoid is symmetric around . Since we want to estimate V_{circ} at R ≃ R_{d}, this higherorder term can be safely ignored, as in the inner galaxy regions.
We now assume that the galaxy is in cylindrical rotation, i.e. . Observationally, it is difficult to obtain information on the rotation velocities above the galaxy plane. A negative velocity gradient in the vertical direction, however, would produce an observable feature: asymmetric line profiles with a tail toward the systemic velocity. This means that a GaussHermite polynomialfit to the line profiles should give high values of the h_{3} term. This effect is observed, for example, in the lagging H I haloes of spiral galaxies (e.g., Fraternali et al. 2002). The stellar, absorptionline profiles of gaspoor dwarfs, instead, are quite symmetric and have  h_{3}  ≲ 0.1 (Halliday et al. 2001; Spolaor et al. 2010; Howley et al. 2013), implying that any vertical velocity gradient is relatively small. It is reasonable, therefore, to assume cylindrical rotation such that α_{z} = 0. Thus, Eq. (A.4) gives σ_{φ} = σ_{z}.
Since we are interested in the inner circularvelocity gradient, we also assume that the galaxy is in solidbody rotation, i.e. . All the Sphs in our sample, indeed, show nearly solidbody rotation curves out to the last measured point (cf. van Zee et al. 2004b) and thus α_{R} = 1. Consequently, Eq. (A.3) gives σ_{φ} = σ_{R} (neglecting the higherorder term). Therefore, using observationallymotivated assumptions, we find that the Sphs in our sample can be approximated as isotropic rotators with σ_{R} = σ_{z} = σ_{φ} = σ_{obs}.
Finally, we assume that the scale height of the galaxy is constant with radius. Thus, we have ∂lnρ/∂lnR = ∂lnΣ/∂lnR, where Σ is the surface density profile (traced by the surface brightness profile). Assuming a Sérsic profile (Sérsic 1963), the asymmetricdriftcorrected circular velocity is given by (A.6)where R_{eff} is the effective radius, n is the Sérsic index, and b_{n} is a constant that depends on n (see Ciotti 1991; Ciotti & Bertin 1999).
For rotating Sphs, the surface brightness profile can be fitted by an exponential law, thus n = 1 and b_{1} = 1.678. We also assume that σ_{obs} is constant with radius, as the observations generally provide only the mean value . Therefore, Eq. (A.6) simplifies to , where R_{d} = 1.678R_{eff} is the exponential scale length. In this case, the error δ_{V/R} on V_{circ}/R is given by (A.7)where D and i are, respectively, the galaxy distance and inclination (cf. with Eq. (3)).
Appendix B: tables
Appendix B.1: Tables B1 and B3: structural and dynamical properties of gasrich dwarfs (BCDs and Irrs)
Column (1) gives the galaxy name. Columns (2)−(4) give the assumed distance, the distance indicator, and the corresponding reference. Columns (5)−(8) give the Rband absolute magnitude M_{R}, the central Rband surface brightness (corrected for inclination), the scale length R_{d}, and the reference for the surface photometry. The structural parameters were derived from an exponential fit to the outer parts of the surface brightness profiles. All the quantities have been corrected for Galactic extinction, but not for internal extinction. Column (9) gives the galaxy inclination, derived by fitting a tiltedring model to the H I velocity field and/or by building 3D modelcubes. Columns (10)−(13) give the circular velocity V_{Rd} at R_{d}, the circular velocity V_{last} at the last measured point, the radius at V_{last}, and the reference for the H I rotation curves. Values of V_{last} in italics indicate rotation curves that do not reach the flat part. Column (14) gives the circularvelocity gradient V_{Rd}/R_{d}.
Sample of starbursting dwarfs: structural and dynamical properties.
Sample of starbursting dwarfs: gas and starformation properties.
Appendix B.2: Tables B2 and B4: gas and star formation properties of gasrich dwarfs (BCDs and Irrs)
Column (1) gives the galaxy name. Columns (2) and (3) give the gas metallicity and the respective reference. Values in italics indicate abundances derived using “strongline” calibrations; we assigned to them a conservative error of 0.2 (cf. Berg et al. 2012). All the other abundances have been derived using the T_{e}method. Columns (4)−(6) give the H I mass, the mean H I surface density within R_{opt} = 3.2R_{d} (corrected for inclination), and the reference for the H I observations. Columns (7)−(9) give the Hα+[N II]equivalent width, the Hα star formation rate (SFR), and the reference for the Hα observations. SFRs have been calculated using the Kennicutt (1998a) calibration and have not been corrected for internal extinction. Columns (10) and (11) give the ratio SFR/M_{bar} and the SFR surface density (). M_{bar} has been estimated using the baryonic TullyFisher relation as calibrated by McGaugh (2012) with an accuracy of ~10%. Values of SFR/M_{bar} in italics indicate galaxies with rotation curves that do not reach the flat part, thus they may be slightly underestimated. Columns (12) and (13) give the global and local gas depletion times τ_{global} and τ_{local}. τ_{global} considers the total atomic gas mass of the galaxy, whereas τ_{local} considers the atomic gas mass within R_{opt}.
Appendix B.3: Table B5: structural and dynamical properties of gaspoor dwarfs (Sphs)
Column (1) gives the galaxy name. Columns (2)−(6) give the Rband absolute magnitude, the inclination i, the central surface brightness (corrected for i), the scale length, and the reference for the surface photometry. The inclination was estimated from the observed ellipticities using Eq. (6) with q_{0} = 0.35. The structural parameters were derived from an exponential fit to the outer parts of the surface brightness profiles. All the quantities have been corrected for Galactic extinction, but not for internal extinction. Columns (7)−(11) give the rotation velocity at R_{d}, the rotation velocity v_{last} at the last measured point, the radius at v_{last}, the mean velocity dispersion, and the reference for the stellar spectroscopy. All rotation velocities have been corrected for inclination. Columns (12)−(14) give the circular velocity at R_{d}, the circular velocity at R_{last}, and the circularvelocity gradient. All the circular velocities have been corrected for asymmetricdrift (see Appendix A).
Sample of irregulars: structural and dynamical properties.
Sample of irregulars: gas and starformation properties.
Sample of rotating spheroidals in the Virgo cluster.
© ESO, 2014
Current usage metrics show cumulative count of Article Views (fulltext 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 4896 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.