arXiv subjects

A. Raichoor

Publications and source records attributed to A. Raichoor.

40 records · Page 3Linked to original sources

arXiv2011

Early-type galaxies at z~1.3. IV. Scaling relations in different environments

We present the Kormendy and mass-size relations for early-type galaxies (ETGs) as a function of environment at z~1.3. Our sample includes 76 visually classified ETGs with masses 10^10 < M/Msun < 10^11.5, selected in the Lynx supercluster and in the GOODS/CDF-S field, 31 ETGs in clusters, 18 in groups and 27 in the field, all with multi-wavelength photometry and HST/ACS observations. The Kormendy relation, in place at z~1.3, does not depend on the environment. The mass-size relation reveals that ETGs overall appear to be more compact in denser environments: cluster ETGs have sizes on average around 30-50% smaller than those of the local universe, and a distribution with a smaller scatter, whereas field ETGs show a mass-size relation with a similar distribution than the local one. Our results imply that (1) the mass-size relation in the field did not evolve overall from z ~ 1.3 to present; this is interesting and in contrast to the trend found at higher masses from previous works; (2) in denser environments, either ETGs have increased their size by 30-50%, on average, and spread their distributions, or more ETGs have been formed within the dense environment from not ETG progenitors or larger galaxies have been accreted to a pristine compact population to reproduce the mass-size relation observed in the local Universe. Our results are driven by galaxies with masses M<2*10^11Msun and those with masses M~10^11Msun follow the same trends that the entire sample. Following Valentinuzzi et al. definition of superdense ETGs, around 35-45% of our cluster sample is made of superdense ETGs.

astro-ph.CO↗

arXiv2011

Star formation and environment in clusters up to z~2.2

The dependence of galaxy star formation activity on environment - especially in clusters - at high redshift is still poorly understood, as illustrated by the still limited number of z>1.4 clusters on the one hand, and by the still debated star formation-density relation at high redshift on the other hand. The zphot~2.2 JKCS041 cluster allows to probe such environmental dependence of star formation activity at an unprecedented combination of redshifts and environments. Its study permits to enlarge the knowledge of high redshift clusters and to put strong leverage on observational constraints for galaxy evolution models. We analyze deep u\astg'r'i'z'JHKs images from the CFHTLS/WIRDS surveys, which cover JKCS041 cluster field. We first estimate photometric redshifts based on multi-wavelength photometry. We then lead a careful analysis to test the presence of a Butcher-Oemler effect. We work on galaxies within 2\timesr200 and with masses >1.34\times10^11 Msun, and use two comparison clusters at z=0 and z=1 of similar mass. We estimate the radial profiles of the fraction of blue galaxies, taking into account the star aging with decreasing redshift. After confirming the high redshift nature of JKCS041, we find no evidence for a Butcher-Oemler effect between z~2.2 and z~0 for galaxies more massive than 1.34\times10^11 Msun. In the cluster center, a change greater than \Deltafblue/\Deltaz=0.16 between z~0 and z~2.2 would be easily detected. We also find that JKCS041 shows a consistent and systematic increase of the fraction of star-forming galaxies with cluster-centric distance, hence with decreasing density, for both a M>1.34\times10^11 Msun selected sample and a lower mass sample. In particular, very few (less than 15%) star-forming galaxies are found within r200/2 among high mass (M>1.34\times10^11 Msun) galaxies. Our results show that the present-day star formation-density relation is already in place at z~2.2.

astro-ph.CO↗

arXiv2011

Early-type galaxies at z~1.3. II. Masses and ages of early-type galaxies in different environments and their dependence on stellar population model assumptions

We have derived masses and ages for 79 early-type galaxies (ETGs) in different environments at z~1.3 in the Lynx supercluster and in the GOODS/CDF-S field using multiwavelength (0.6-4.5 $μ$m; KPNO, Palomar, Keck, HST, Spitzer) datasets. At this redshift the contribution of the TP-AGB phase is important for ETGs, and the mass and age estimates depend on the choice of the stellar population model used in the spectral energy distribution fits. We describe in detail the differences among model predictions for a large range of galaxy ages, showing the dependence of these differences on age. Current models still yield large uncertainties. While recent models from Maraston and Charlot & Bruzual offer better modeling of the TP-AGB phase with respect to less recent Bruzual & Charlot models, their predictions do not often match. The modeling of this TP-AGB phase has a significant impact on the derived parameters for galaxies observed at high-redshift. Some of our results do not depend on the choice of the model: for all models, the most massive galaxies are the oldest ones, independent of the environment. When using Maraston and Charlot & Bruzual models, the mass distribution is similar in the clusters and in the groups, whereas in our field sample there is a deficit of massive (M $\gtrsim$ 10^11 Msun) ETGs. According to those last models, ETGs belonging to the cluster environment host on average older stars with respect to group and field populations. This difference is less significant than the age difference in galaxies of different masses.

astro-ph.CO↗

arXiv2011

Early-Type galaxies at z ~ 1.3. III. On the dependence of Formation Epochs and Star Formation Histories on Stellar Mass and Environment

We study the environmental dependence of stellar population properties at z ~ 1.3. We derive galaxy properties (stellar masses, ages and star formation histories) for samples of massive, red, passive early-type galaxies in two high-redshift clusters, RXJ0849+4452 and RXJ0848+4453 (with redshifts of z = 1.26 and 1.27, respectively), and compare them with those measured for the RDCS1252.9-2927 cluster at z=1.24 and with those measured for a similarly mass-selected sample of field contemporaries drawn from the GOODS-South Field. Robust estimates of the aforementioned parameters have been obtained by comparing a large grid of composite stellar population models with extensive 8-10 band photometric coverage, from the rest-frame far-ultraviolet to the infrared. We find no variations of the overall stellar population properties among the different samples of cluster early-type galaxies. However, when comparing cluster versus field stellar population properties we find that, even if the (star formation weighted) ages are similar and depend only on galaxy mass, the ones in the field do employ longer timescales to assemble their final mass. We find that, approximately 1 Gyr after the onset of star formation, the majority (75%) of cluster galaxies have already assembled most (> 80%) of their final mass, while, by the same time, fewer (35%) field ETGs have. Thus we conclude that while galaxy mass regulates the timing of galaxy formation, the environment regulates the timescale of their star formation histories.

astro-ph.CO↗