A. Rawat

New spectroscopic redshifts from the CDFS and a test of the cosmological relevance of the GOODS-South field

(Abbrev.) This paper prepares a series of papers analysing the Intermediate MAss Galaxy Evolution Sequence (IMAGES) up to z=1. Intermediate mass galaxies (MJ <=-20.3) are selected from the Chandra Deep Field South (CDFS) for which we identify a serious lack of spectroscopically determined redshifts..... We have spectroscopically identified 691 objects including 580 gal., 7 QSOs, and 104 stars. This study provides 531 new redshifts in the CDFS. It confirms the presence of several large scale structures in the CDFS. To test the impact of these structures in the GOODS-South field, we ... compare the evolution of rest-frame U, B, V and K galaxy luminosity densities to that derived from the CFRS. The CDFS field shows a significant excess of luminosity densities in the z=0.5-0.75 range, which increases with the wavelength, reaching up to 0.5 dex at 2.1 um. Stellar mass and specific star formation evolutions might be significantly affected by the presence of the peculiar large scale structures at z= 0.668 and at z= 0.735, that contain a significant excess of evolved, massive galaxies when compared to other fields. This leads to a clear warning to results based on the CDFS/GOODS South fields, especially those related to the evolution of red luminosity densities, i.e. stellar mass density and specific star formation rate. Photometric redshift techniques, when applied to that field, are producing quantities which are apparently less affected by cosmic variance (0.25 dex at 2.1 um), however at the cost of the difficulty in disentangling between evolutionary and cosmic variance effects.

HST/WFPC2 morphologies and bar structures of field galaxies at 0.4< z< 1 ⋆

To address how the galaxy Hubble sequence is established and what physical processes are involved, we studied morphological properties and internal structures of field galaxies in the past (0.4 =10^11 L_sun). Here we presented morphological classification of a parallel 75 non-LIRG sample. Our examination revealed that a significant fraction of the galaxies shows remarkable morphological evolution, most likely related to the present-day spiral galaxies. Comparison of the morphological properties between LIRGs and non-LIRGs shows that the LIRGs contain a higher fraction of ongoing major mergers and systems with signs of merging/interaction. This suggests that the merging process is one of the major mechanisms to trigger star formation. We found that spiral LIRGs probably host much fewer bars than spiral non-LIRGs, suggesting that a bar is not efficient in triggering violent star formation. Differing from Abraham et al. (1999), no dramatic change of the bar frequency is detected up to redshift ~0.8. The bar frequency of the distant spirals is similar to (and may be higher than) the present-day spirals in the rest-frame

Toward a robust estimate of the merger rate evolution using near-IR photometry

B

Unravelling the morphologies of Luminous Compact Galaxies using the HST/ACS GOODS survey

band. We conclude that bar-driven secular evolution is not a major mechanism to drive morphological evolution of field galaxies, especially their bulge formation, which is more likely related to multiple intense star formation episodes during which the galaxies appear as LIRGs (Hammer et al. 2005).

Rest-Frame UV Versus Optical Morphologies of Galaxies Using Sérsic Profile Fitting: The Importance of Morphological K-Correction

We use a combination of deep, high angular resolution imaging data from the CDFS (HST/ACS GOODS survey) and ground-based near-IR Ks images to derive the evolution of the galaxy major merger rate in the redshift range 0.2 ≤ z≤ 1.2. We select galaxies solely on the basis of their J-band rest-frame absolute magnitude, which is a good tracer of the stellar mass. We find steep evolution with redshift, with the merger rate ∝(1 + z)3.43 ± 0.49 for optically selected pairs and ∝(1 + z)2.18 ± 0.18 for pairs selected in the near-IR. Our result is unlikely to be affected by luminosity evolution that is relatively modest when using rest-frame J-band selection. The apparently more rapid evolution that we find in the visible is likely caused by biases relating to incompleteness and spatial resolution affecting the ground-based near-IR photometry, underestimating pair counts at higher redshifts in the near-IR. The major merger rate was ~5.6 times higher at z ~ 1.2 than at the current epoch. Overall, 41% × (0.5 Gyr/τ) of all galaxies with MJ ≤ − 19.5 have undergone a major merger in the last ~8 Gyr, where τ is the merger timescale. Interestingly, we find no effect on the derived major merger rate due to the presence of the large-scale structure at z = 0.735 in the CDFS.

Rest frame UV vs. optical morphologies of galaxies: Important implications to high-z results

Context. Luminous Compact Galaxies (LCGs) (M B 15 A) constitute one of the most rapidly evolving galaxy populations over the last ∼8 Gyr history of the universe. Due to their inherently compact sizes, any detailed quantitative analysis of their morphologies has proved to be difficult in the past. Hence, the morphologies and thereby the local counterparts of these enigmatic sources have been hotly debated. Aims. Our aim is to use the high angular resolution, deep, multiband HST/ACS imaging data, from the HST/ACS GOODS survey, to study the quantitative morphology of a complete sample of LCGs in the redshift range 0.5 ≤ z < 1.2. Methods. We have derived structural parameters for a representative sample of 39 LCGs selected from the GOODS-S HST/ACS field, using full 2-dimensional surface brightness profile fitting of the galaxy images in each of the four filters available. B 435w - z 850LP color maps are constructed for the sample to aid in the morphological classification. We then use the rest frame B band bulge flux fraction (BIT) to determine the morphological class of galaxies which are well fit by a bulge+disk two dimensional structure. Mergers were essentially identified visually by the presence of multiple maxima of comparable intensity in the rest frame B band images, aided by the color maps to distinguish them from HII regions. We also make use of the Spitzer 24 μm source catalog of sources in the CDFS to derive the dust enshrouded star formation rates (SFR) for some of the sample LCGs Results. We derive the following morphological mix for our sample of intermediate redshift LCGs: Mergers: ∼36%, Disk dominated: ∼22%, S0: ∼20%, Early types: ∼7%, Irr/tadpole: ∼15%. We establish that our sample LCGs are intermediate mass objects with stellar mass ranging from 9.44 < Log 10 (M/M ⊙ ) < 10.96, with a median mass of Log 10 (M/M ⊙ ) = 10.32. We also derive SFR values ranging from a few to ∼65 M ⊙ /year as expected for this class of objects. We find that LCGs account for ∼26% of the M B ≤ -20 galaxy population in the redshift range 0.5 < z ≤ 1.2. We estimate a factor∼ 11 fall in the comoving number density of blue LCGs from redshifts 0.5 < z < 1.2 to the current epoch, even though this number is subject to large uncertainties given the small sample size at zero redshift available from the literature. Conclusions. The strong redshift evolution exhibited by LCGs, and the fact that a significant fraction of LCGs are in merging systems, seem to indicate that LCGs might be an important phase in the hierarchical evolution of galaxies. We envisage that some of the LCGs that are classified as merging systems, might go on to rebuild their disks and evolve into disk galaxies in the local universe.

The evolution of the near-infrared Tully-Fisher relation over the last 6 Gyr

We show a comparison of the rest-frame UV morphologies of a sample of 162 intermediate-redshift (z median = 1.02) galaxies with their rest-frame optical morphologies. We select our sample from the deepest near-UV image obtained with the Hubble Space Telescope (HST) using the Wide Field Planetary Camera 2 (WFPC2; F300W) as part of the parallel observations of the Hubble Ultra Deep Field campaign overlapping with the HST/ACS Great Observatories Origins Deep Survey data set. We perform single-component Sersic fits in both WFPC2/F300W (rest-frame UV) and ACS/F850LP (rest-frame optical) bands and deduce that the Sersic index n is estimated to be smaller in the rest-frame UV compared to the rest-frame optical, leading to an overestimation of the number of merger candidates by ~40%-100% compared to the rest-frame optical depending upon the cutoff in n employed for identifying merger candidates. This effect seems to be dominated by galaxies with low values of n(F300W) ≤ 0.5 that have a value of n(F850LP) ~ 1.0. We argue that these objects are probably clumpy star-forming galaxies or minor mergers, both of which are essentially contaminants, if one is interested in identifying major mergers. In addition, we also find evidence that the axis ratio b/a is lower, i.e., ellipticity (1 – b/a) is higher in rest-frame UV compared to the rest-frame optical. Moreover, we find that in the rest-frame UV, the number of high ellipticity (e ≥ 0.8) objects are higher by a factor of ~2.8 compared to the rest-frame optical. This indicates that the reported dominance of elongated morphologies among high-z Lyman Break Galaxies might just be a bias related to the use of rest-frame UV data sets in high-z studies.