IR colors and sizes of faint galaxies

Citation
P. Saracco et al., IR colors and sizes of faint galaxies, ASTRON ASTR, 349(3), 1999, pp. 751-764
Citations number
71
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Space Sciences
Journal title
ASTRONOMY AND ASTROPHYSICS
ISSN journal
0004-6361 → ACNP
Volume
349
Issue
3
Year of publication
1999
Pages
751 - 764
Database
ISI
SICI code
0004-6361(199909)349:3<751:ICASOF>2.0.ZU;2-B
Abstract
We present J and Ks band galaxy counts down to J=24 and Ks=22.5 obtained wi th the new infrared imager/spectrometer, SOFI, at the ESO New Technology Te lescope. The co-addition of short, dithered, images led to a total exposure time of 256 and 624 minutes respectively, over an area of similar to 20 ar cmin(2) centered on the NTT Deep Field. The total number of sources with S/ N> 5 is 1569 in the J sample and 1025 in the Ks-selected sample. These are the largest samples currently available at these depths. A dlogN/dm relatio n with slope of similar to 0.36 in J and similar to 0.38 in Ks is found wit h no evident sign of a decline at the magnitude limit. The observed surface density of "small" sources is much lower than "large" ones at bright magni tudes and rises more steeply than the large sources to fainter magnitudes. Fainter than J similar to 22.5 and Ks similar to 21.5, small sources domina te the number counts. Galaxies get redder in J-K down to J similar to 20 an d Ks similar to 19. At fainter magnitudes, the median color becomes bluer w ith an accompanying increase in the compactness of the galaxies. We show th at the blue, small sources which dominate the faint IR counts are not compa tible with a high redshift (z > 1) population. On the contrary, the observe d color and compactness trends, together with the absence of a turnover at faint magnitudes and the dominance of small sources, can be naturally expla ined by an increasing contribution of sub-L* galaxies when going to fainter apparent magnitudes. Such evidence strongly supports the existence of a st eeply rising (alpha << - 1) faint end of the local infrared luminosity func tion of galaxies - at least for luminosities L < 0.01L*.