Polar-ring galaxies: the SDSS view on the symbiotic galaxies

Polar-ring galaxies are multi-spin systems, showing star formation in a blue late-type component, perpendicular to a red early-type one, revealing how galaxy formation can sometimes occur in successive steps. We perform two-dimensional decomposition in the $g$, $r$, $i$ bandpasses of 50 polar-ring galaxies (PRGs) from the Sloan Digital Sky Survey. Each object was fit with a S\'ersic host galaxy and a S\'ersic ring. Our general results are: (i) The central (host) galaxies of the PRGs are non-dwarf sub-$L^{\ast}$ galaxies with colors typical for early-type galaxies. (ii) Polar structures in our sample are, on average, fainter and bluer than their host galaxies. (iii) In most galaxies, the stellar mass M$_*$ of the polar component is not negligible in comparison with that of the host. (iv) The distributions of the host galaxies on the size -- luminosity and Kormendy diagrams are shifted by $\sim 1^m$ to fainter magnitudes in comparison with E/S0 galaxies. It means that the PRGs hosts are more similar to quenched disks than to ordinary early-type galaxies. (v) All the PRGs in our sample are detected in mid-infrared by WISE, and we derive from the 22$\mu$m luminosity their star formation rate (SFR). Their SFR/M$_*$ ratio is larger than for the early-type galaxy sample of Atlas$^{\rm 3D}$, showing that the star forming disk brings a significant contribution to the new stars. Globally, PRGs appear frequently on the green valley in the mass-color diagram, revealing the symbiotic character between a red-sequence host and a blue cloud ring.Comment: 8 pages, 11 figures, accepted for publication in MNRA

On the global structure of distant galactic disks

Radial and vertical profiles are determined for a sample of 34 edge-on disk galaxies in the HDFs, selected for their apparent diameter larger than 1.3 arcsec and their unperturbed morphology. The thickness and flatness of their galactic disks are determined and discussed with regard to evolution with redshift. We find that sub-L* spiral galaxies with z \sim 1 have a relative thickness or flatness (characterized by h_z/h the scaleheight to scalelength ratio) globally similar to those in the local Universe. A slight trend is however apparent, with the h_z/h flatness ratio larger by a factor of \sim 1.5 in distant galaxies if compared to local samples. In absolute value, the disks are smaller than in present-day galaxies. About half of the z \sim 1 spiral disks show a non-exponential surface brightness distribution.Comment: 13 pages, 8 figures, accepted in A and

Molecular gas and star formation in M81

We present IRAM 30m observations of the central 1.6 kpc of the spiral M81 galaxy. The molecular gas appears weak and with an unusual excitation physics. We discuss a possible link between low CO emission and weak FUV surface brightness.Comment: 2 pages, 2 figures, to appear in "Pathways through an eclectic Universe", J. H. Knapen, T. J. Mahoney, and A. Vazdekis (Eds.), ASP Conf. Ser., 200

Are truncated stellar disks linked to the molecular gas density?

We know that the slope of the radial, stellar light distribution in galaxies is well described by an exponential decline and this distribution is often truncated at a break radius ($R_{br}$). We don't have a clear understanding for the origin of these outer truncations and several hypotheses have been proposed to explain them. We want to test the various theories with direct observations of the cold molecular gas for a few truncated galaxies in comparison with the non-truncated ones. The answer to the existence of a possible link between truncated stellar disks and the molecular gas density cannot be obtained from CO maps in the literature, because so far there are no galaxies with a clear truncation observed in CO at high resolution.Comment: 3 pages, 6 figures, to appear in Astrophysics and Space Science (Apss), special issue of "Science with ALMA: a new era for Astrophysics" conference, ed. Dr. Bachille