Free Access
Volume 527, March 2011
Article Number A23
Number of page(s) 28
Section Extragalactic astronomy
Published online 20 January 2011

Online material

Appendix A: Comments on individual objects

IC 1459. At HST resolution, Lauer et al. (2005) classified this galaxy as a starting, dusty nuclear ring and, based on Hα+[NII] WFPC2 images, Verdoes Kleijn et al. (2000) identify an ionized gas disk with PA 37° and inclination 60° following what is found by Goudfrooij et al. (1990) on larger scales (100 arcsec). Here we report a residual Hα emission with a central source and a rather biconical distribution extended  ~500 pc at PA 37° (Fig. 2). At soft X-ray energies (0.3–2 keV), it extends along the same direction as in Hα HST data (Fig. 6).

NGC 315. A compact unresolved source of ionized gas on top of a dusty disk, together with an extension of the disk of 200 pc at PA 49°, is detected (see Fig. 2; see also Verdoes-Keijn et al. 1999). The high spatial resolution provided by Chandra imaging allowed detection of the X-ray jets (Donato et al. 2004; Worrall et al. 2003, 2007; Gonzalez-Martin et al. 2009). Soft X-rays extend along the axes of the jet and the host galaxy (Fig. 6).

NGC 2639. At HST resolution, its Hα shows an elongated asymmetrically extended structure at PA –29°, but nuclear compact source is not identifiable. It also shows extended filaments as more prominent towards the NW. The SE region may be obscured by dust. The SD images and the broad band data show a rather dusty morphology (see Fig. 2; and Simões Lopez et al. 2007).

NGC 2681. The Hα emission image shows a central source with extended emission throughout the central spiral structure with major axis at PA 40° and a radial extension of 4 arcsec ( ~ 440 pc). Spiral dust lanes are clearly detected in the SD image (Fig. 2). Broad agreement is found in the elongation of soft X-ray and Hα emissions (Fig. 6).

NGC 2787. On the HST SD images, a near-nuclear dust lane is clearly resolved into a spectacular set of concentric, elliptical dust rings, covering a radial range of 510 arcsec (see also Shields et al. 2007; Simões-Lopes et al. 2008; Gonzalez Delgado et al. 2008). In Hα, a nuclear component has been detected, in good agreement with Dai & Wang (2009). An elongation at PA 49° can also be identified, which is perpendicular to the major axis of the galaxy (Fig. 2). Soft X-rays roughly follow the Hα emission (Fig. 6).

NGC 2841. At HST resolutions, NGC 2841 shows a rather face-on ring-like structure and a clearly identified unresolved nuclear source. An small NLR can be identified at PA of 90°. Dust morphology becomes apparent from the SD image (Fig. 2). Soft X-rays extend along two main axes, one following the hard X-ray emission (PA about 10) and the other one close to that of the Hα emission (Fig. 6).

NGC 3226. This galaxy shows a bright nucleus with some clear evidence of dusty environment in the SD image (see also Gonzalez Delgado et al. 2008). In Hα it shows an extended morphology quite similar to what is observed in continuum (Fig. 2). At X-ray frequencies it shows a compact structure both at soft and hard energies. The Hα, however, seems to suggest an outflow-like morphology emerging from the compact nucleus (Fig. 6).

NGC 3245. The Hα image shows a kidney-like structure slightly brighter to the N, with a nuclear, unresolved source (see also (Gonzalez Delgado et al. 2008; Walsh et al. 2008). Kinematical data from Walsh et al. (2008) support our outflow classification. The W dust structure is clearly appreciated in the SD image. (Fig. 2). One of the two axes shown by the soft X-ray contours follows the Hα emission (Fig. 6).

NGC 3379. An extended structure emerging from the nucleus can be appreciated although the S/N on the Hα image is low. A tiny dust lane crosses the nuclear regions at PA  − 50° in SD (Fig. 2). At HST resolution Lauer et al. (2005), based on the F555W filter, classified this galaxy without a clear nuclei but with a dusty nuclear ring morphology. Shapiro et al. (2006) report a well-defined disk of emission at Hα with PA 118. The morphology of the soft X-ray contours is quite complex, but rough agreement with the extended Hα emission is found (Fig. 6).

NGC 3607. The Hα image shows a clearly nuclear, unresolved source and diffuse emission following what appears to be an inclined disk. The strong dust lanes visible in the SD images obscure the Hα emission (Fig. 2). Lauer et al. (2008) suggest that it contains a dusty outer disk that is dynamically old and that appears to transition rapidly but smoothly at the centre to a second gas disk that is perpendicular to the first and is seen nearly edge-on. This inclined disk seems to be settling onto a nuclear ring. Except for the the outermost contours, the soft X-ray emission is elongated in the Hα emission (Fig. 6).

NGC 3623. Hα emission has been detected, extending  ~130 pc at PA−10°. Inside the more extended structure an inner disk is seen to extend 30 pc along PA 53°. Large-scale dust lanes clearly appear in the SD image (Fig. 2).

NGC 3627. The Hα data (Fig. 2) do not show a well-defined nuclear source, most probably because the dust lane crosses the nuclear region in the direction NS and obscures the SE-NW elongated extended emission (see the SD image). Gonzalez-Delgado et al. (2008) report from HST data that chaotic dust lanes and several compact sources are identified at the centre.

NGC 3998. The Hα image (Fig. 2) shows a 100 pc extended structure surrounding a compact nucleus. The major axis of this extension is oriented along PA = 0° (see also Pogge et al. 2000). The SD image shows little indication of dust in the nuclear region, in good agreement with Gonzalez Delgado et al. (2008). Soft X-rays are elongated in the same direction as the Hα emission (Fig. 6).

NGC 4036. The HST Hα image (Fig. 2) shows, on top of a well-identified nucleus, a complicated filamentary and clumpy structure, with an extension of 390 pc at PA 63°, already reported by Pogge et al. (2000) and Dai & Wang (2009) (see also the SD image). Walsh et al. (2009) show there is a gas velocity gradient of  ~300 km s-1 across the inner 0.2", compatible with the outflow-like structure apparent in the ionized gas. The soft X-ray emission appears to follow the Hα emission (Fig. 6).

NGC 4111. A rather knotty morphology surrounding a clear nuclear source is observed, embedded in a diffuse halo. This morphology is interpreted as a core-halo structure detected at HST resolution both with medium size filters (Simões Lopes et al. 2007) and narrow band Hα data (Dai & Wang 2009). A crossing dust structure is seeing perpendicular to the disk main plane (see SD image). Soft X-ray contours are elongated along the same PA as the Hα emission (Fig. 6).

NGC 4278.A clear core-halo morphology is shown by its Hα emission on the top of a very faint continuum (Fig. 2). This emission seems to follow what is observed in the soft X-ray emission (Fig. 6).

NGC 4314. The Hα image (Fig. 2) shows both an unresolved nucleus and a number of HII regions tracing the star formation ring. The same features are traced well by the SD image, where the spiral dust lanes associated with the ring are conspicuous (see also Gonzalez Delgado et al. 2008). At soft energies, its emission follows the star-forming regions observed in Hα (Fig. 6).

NGC 4374. The Hα image (Fig. 2) shows an inclined gas disk surrounding the nucleus. This emission gas structure takes the form of filaments that extend roughly EW and NS (see also (Pogge et al. 2000). The dust structure clearly appears in the SD image, where the nucleus is seen in the centre of the dust lane to the S. The soft X-ray contours are roughly aligned with the ionized gas (Fig. 6).

NGC 4438. Gonzalez Delgado et al. (2008) define NGC 4438 as a galaxy with a very perturbed central morphology, and strong dust lanes cross the centre along PA 0° obscuring the E side of the galaxy (see the SD image). The Hα image (Fig. 2) shows a ring-like structure where a clear knot is seen in the SE region coincident with the continuum nucleus. The other side would remain invisible due to obscuration by dust. Two plumes can be seen to the N and SW extending about 150 pc in both directions. This is one of the clearest examples of a candidate of nuclear outflow, bubble structures, as defined in Veilleux and Brandt (2007). Soft X-rays are aligned with the Hα emission (Fig. 6).

NGC 4486. The Hα image (Fig. 2) shows a compact source with filaments that resemble an outflow from the nucleus (see also Pogge et al. 2000; Dai & Wang 2009). As already noticed by Pogge et al. (2000), the conspicuous jet is clearly visible in the continuum images (see SD) disappears in the Hα continuum substracted map. Soft X-rays are misaligned with respect to Hα emission, the former following the jet axis (Fig. 6).

NGC 4552. At HST resolution the Hα data show a compact unresolved nuclear source located at the centre of a symmetric, extended emission in a disk-like structure. No trace of dust-lanes is seen in the SD image (Fig. 2). Soft X-rays roughly follow the Hα emission (Fig. 6).

NGC 4579. The Hα emission (Fig. 2) traces a bright nuclear point source surrounded by complex clumpy and filamentary emission (see also Pogge et al. 2000). The higher ionization gas traced by [OIII] (Fig. 2) is composed of a compact source and a filamentary, jet-like structure towards the NE. Walsh et al. (2008) have shown that the gas is not in regular rotation, displaying two kinematical components with a velocity separation of 450 km s-1, being consistent with an outflow from the nucleus. The dust lanes seen in the SD image conform to a mainly chaotic structure, together with a much stronger offset linear feature that goes at PA ≈ 45° on the W side. Soft X-ray contours follow the Hα emission on large scales. There is a hint of an extension of hard X-rays along the PA of the [OIII] jet-like feature (Fig. 6).

NGC 4594. The Hα image (Fig. 2) shows a compact nuclear source, together with fainter emission extending along the EW direction in a bar-like morphology, with two spiral arms emerging from it and a total extension of 300 pc. The kinematical data by Walsh et al. (2008) show organized motion consistent with rotation but with significant irregularities in the nucleus. A strong velocity gradient and decoupled kinematics between gas and stars were found by Emsellem & Ferruit (2000). An overall extension of soft X-rays is seen along the same axis as the extended ionized gas (Fig. 6).

NGC 4636. The Hα data (Fig. 2) show a central compact source and a very faint ring-like structure more clearly visible in the S region of the galaxy (see also Simões Lopes et al. 2007; and Dai & Wang 2009).Towards the N, a more prominent Hα emission is seen with a clear outflow-like morphology. This morphology seems to follow the soft X-ray data (Fig. 6).

NGC 4676A and B. The Mice. The Hα images (Fig. 2) show a very clumpy and irregular structure in both galaxies . In galaxy B a more conspicuous knotty structure is visible. One of the knots coincides with the nucleus. In galaxy A, however, a more diffuse emission is seen. Central dust lanes are much stronger in galaxy B, seen in the SD images (see also Laine et al. 2003). The soft X-ray contours are unrelated to the extended Hα emission in both galaxies (Fig. 6).

NGC 4696. Hα imaging (Fig. 2) shows a clear nuclear source with elongated extended emission along PA 47°, and larger filamentary structures towards the W may resemble outflows out of the nucleus.Crawford et al. (2005) also report a filamentary structure shared by the Hα and soft X-ray emission (see also our Fig. 6).

NGC 4736. The Hα image shows a circumnuclear spiral structure of extension 200 pc. Dust lanes in spiral arms are traced in the SD image (Fig. 2). Gonzalez Delgado et al. (2008) suggest there are spiral dust lanes down the nucleus and a compact nuclear stellar cluster. Despite the complexity of the soft X-ray emission, rough agreement is found in the overall shape of both images (Fig. 6).

NGC 5005. Hα data (Fig. 2) show a very asymmetric emission with a wide-angle cone-like structure extending to the SE (see Pogge et al. 2000; and Dai & Wang 2009), perpendicular to the major axis of the galaxy. A strong dust lane crosses the galaxy from E to W, offset from the nucleus (see the SD image and Gonzalez Delgado et al. 2008).

NGC 5055. Its Hα image (Fig. 2) shows a nuclear source and extended emission along PA 110°. A floculent spiral structure, stronger to the S, is visible in the SD image (see also Gonzalez Delgado et al. 2008). Soft X-rays and Hα emission are extended in roughly the same direction (Fig. 6).

NGC 5846. The Hα image (Fig. 2) shows a compact nucleus and diffuse emission resembling a very wide outflow extending up to 2′′ in the W direction. This strong asymmetry cannot be explained by dust absorption (see the SD image). No correlation is seen between Hα and soft X-ray emission (Fig. 6).

NGC 5866. The Hα image shows an extremely faint nucleus on top of a very dusty structure along PA –45° strongly obscuring the nucleus (see also the SD image), which hampers either any classification of the emission (Fig. 2) or any comparison with the soft X-ray emission (Fig. 6).

thumbnail Fig. 2

Images of Hα (left) and SD (right). Top is north and east to the left. The units of the plots are arcsecs. For clarity contours above 3σ levels have been plotted in the Hα images. For the outflow candidates, the contour for which Req was estimated is also plotted with a black or a white thick line. The position angle of the host major axis has been taken from the ned database and is shown as a solid line.

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thumbnail Fig. 6

X-ray contours are overplotted onto the Hα images. Top is north and east is left. The units of the plots are arcsecs.Soft (0.6–0.9 keV) X-rays contours are plotted in black and hard (4.5–8 keV) X-rays in red.

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© ESO, 2011

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