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Register a new userClustering Properties of restframe UV selected galaxies I: the correlation length derived from GALEX data in the local Universe
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We present the first measurements of the angular correlation function of galaxies selected in the far (1530 A) and near (2310 A) Ultraviolet from the GALEX survey fields overlapping SDSS DR5 in low galactic extinction regions. The area used covers 120 sqdeg (GALEX - MIS) down to magnitude AB = 22, yielding a total of 100,000 galaxies. The mean correlation length is ~ 3.7 pm 0.6 Mpc and no significant trend is seen for this value as a function of the limiting apparent magnitude or between the GALEX bands. This estimate is close to that found from samples of blue galaxies in the local universe selected in the visible, and similar to that derived at z ~ 3 for LBGs with similar rest frame selection criteria. This result supports models that predict anti-biasing of star forming galaxies at low redshift, and brings an additional clue to the downsizing of star formation at z<1.
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We analyze the clustering properties of ultraviolet selected galaxies by using GALEX-SDSS data at z<0.6 and CFHTLS deep u imaging at z=1. These datasets provide a unique basis at z< 1 which can be directly compared with high redshift samples built with similar selection criteria. We discuss the dependence of the correlation function parameters (r0, delta) on the ultraviolet luminosity as well as the linear bias evolution. We find that the bias parameter shows a gradual decline from high (b > 2) to low redshift (b ~ 0.79^{+0.1}_{-0.08}). When accounting for the fraction of the star formation activity enclosed in the different samples, our results suggest that the bulk of star formation migrated from high mass dark matter halos at z>2 (10^12 < M_min < 10^13 M_sun, located in high density regions), to less massive halos at low redshift (M_min < 10^12 M_sun, located in low density regions). This result extends the ``downsizing picture (shift of the star formation activity from high stellar mass systems at high z to low stellar mass at low z) to the dark matter distribution.
We present the results of a determination of the galaxy luminosity function at ultraviolet wavelengths at redshifts of $z=0.0-0.1$ from GALEX data. We determined the luminosity function in the GALEX FUV and NUV bands from a sample of galaxies with UV magnitudes between 17 and 20 that are drawn from a total of 56.73 deg^2 of GALEX fields overlapping the b_j-selected 2dF Galaxy Redshift Survey. The resulting luminosity functions are fainter than previous UV estimates and result in total UV luminosity densities of 10^(25.55+/-0.12) ergs s^-1 Hz^-1 Mpc^-3 and 10^(25.72+/-0.12) ergs s^-1 Hz^-1 Mpc^-3 at 1530 Ang. and 2310 Ang., respectively. This corresponds to a local star formation rate density in agreement with previous estimates made with H-alpha-selected data for reasonable assumptions about the UV extinction.
Disk scale length and central surface brightness for a sample of about 29955 bright disk galaxies from the Sloan Digital Sky Survey have been analysed. Cross correlation of the SDSS sample with the LEDA catalogue allowed us to investigate the variation of the scale lengths for different types of disk/spiral galaxies and present distributions and typical trends of scale lengths all the SDSS bands with linear relations that indicate the relation that connect scale lengths in one passband to another. We use the volume corrected results in the r-band and revisit the relation between these parameters and the galaxy morphology. The derived scale lengths presented here are representative for a typical galaxy mass of 10^10.8 solarmasses, and the RMS dispersion is larger for more massive galaxies. We analyse the scale-length-central disk brightness plane and further investigate the Freeman Law and confirm that it indeed defines an upper limit for disk central surface brightness in bright disks (r<17.0), and that disks in late type spirals (T > 6) have fainter central surface brightness. Our results are based on a sample of galaxies in the local universe (z< 0.3) that is two orders of magnitudes larger than any sample previously studied, and deliver statistically significant results that provide a comprehensive test bed for future theoretical studies and numerical simulations of galaxy formation and evolution.
We measure the UV-optical color dependence of galaxy clustering in the local universe. Using the clean separation of the red and blue sequences made possible by the NUV - r color-magnitude diagram, we segregate the galaxies into red, blue and intermediate green classes. We explore the clustering as a function of this segregation by removing the dependence on luminosity and by excluding edge-on galaxies as a means of a non-model dependent veto of highly extincted galaxies. We find that xi (r_p, pi) for both red and green galaxies shows strong redshift space distortion on small scales -- the finger-of-God effect, with green galaxies having a lower amplitude than is seen for the red sequence, and the blue sequence showing almost no distortion. On large scales, xi (r_p, pi) for all three samples show the effect of large-scale streaming from coherent infall. On scales 1 Mpc/h < r_p < 10 Mpc/h, the projected auto-correlation function w_p(r_p) for red and green galaxies fits a power-law with slope gamma ~ 1.93 and amplitude r_0 ~ 7.5 and 5.3, compared with gamma ~ 1.75 and r_0 ~ 3.9 Mpc/h for blue sequence galaxies. Compared to the clustering of a fiducial L* galaxy, the red, green, and blue have a relative bias of 1.5, 1.1, and 0.9 respectively. The w_p(r_p) for blue galaxies display an increase in convexity at ~ 1 Mpc/h, with an excess of large scale clustering. Our results suggest that the majority of blue galaxies are likely central galaxies in less massive halos, while red and green galaxies have larger satellite fractions, and preferentially reside in virialized structures. If blue sequence galaxies migrate to the red sequence via processes like mergers or quenching that take them through the green valley, such a transformation may be accompanied by a change in environment in addition to any change in luminosity and color.
Shell galaxies are widely considered the debris of recent accretion/merging episodes. Their high frequency in low density environment suggests that such episodes could be among the driver of the early-type galaxy secular evolution. We present far and near UV (FUV and NUV respectively hereafter) GALEX photometric properties of a sample of shell galaxies.
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