M. Huertas-Company

A robust morphological classification of high-redshift galaxies using support vector machines on seeing limited images. II. Quantifying morphological k-correction in the COSMOS field at 1

We quantify the effects of \emph{morphological k-correction} at

The role of environment in the morphological transformation of galaxies in 9 rich intermediate redshift clusters

11

Morphological evolution of z∼ 1 galaxies from deep K-band AO imaging in the COSMOS deep field

could be underestimating the elliptical population. [abridged]

A robust morphological classification of high-redshift galaxies using support vector machines on seeing limited images I. Method description

Context. Rich clusters offer a unique laboratory for studying the effects of local environment on the morphological transformation of galaxies moving from the blue star-forming cloud to the red passive sequence. Due to the high-density, any environmental process should be more pronounced there compared to the field population. Aims. Ideally, we would like to reconstruct the evolution of a single, hypothetical representative galaxy as it enters the cluster. For that purpose wide-field imaging is crucial to probe a wide range of densities and environments (from the core to the outskirts) and isolate this way, the different physical processes which are responsible of the migration from the blue-cloud to the red-sequence. Methods. We analyze a sample of 9 massive clusters at 0.4 9.5). Results. We find that the red sequence is already in place at z ∼ 0.5 and it is mainly composed of very massive (log(M/M ⊙ ) > 11.3) early-type galaxies. These massive galaxies seem to be already formed when they enter the cluster, probably in infalling groups, since the fraction remains constant with the cluster radius. Their presence in the cluster center could be explained by a segregation effect reflecting an early assembly history. Any evolution that takes place in the galaxy cluster population occurs therefore at lower masses (10.3 < log(M/M ⊙ ) < 11.3). For these galaxies, the evolution, is mainly driven by galaxy-galaxy interactions in the outskirts as revealed by the T - Σ relation. Finally, the majority of less massive galaxies (9.5 < log(M/M ⊙ ) < 10.3) are late-type galaxies at all locations, suggesting that they have not started the morphological transformation yet even if this low mass bin might be affected by incompleteness.

A robust morphological classification of high-redshift galaxies using support vector machines on seeing limited images

Context. We present the results of an imaging program of distant galaxies (z ∼ 0.8) at high spatial resolution (∼0.1 �� ) aiming at studying their morphological evolution. We observed 7 fields of 1 � × 1 � with the NACO Adaptive Optics system (VLT) in Ks (2.16 µm) band with typical V ∼ 14 guide stars and 3 h integration time per field. Observed fields are selected within the COSMOS survey area, in which multi-wavelength photometric and spectroscopic observations are ongoing. High angular-resolution K-band data have the advantage of probing old stellar populations in the rest-frame, enabling a determination of galaxy morphological types unaffected by recent star formation, which are more closely linked to the underlying mass than classical optical morphology studies (HST). Adaptive optics on ground based telescopes is the only method today for obtaining such a high resolution in the K-band, but it suffers from limitations since only small fields are observable and long integration times are necessary. Aims. In this paper we show that reliable results can be obtained and establish a first basis for larger observing programs. Methods. We analyze the morphologies by means of B/ D( bulge/disk) decomposition with GIM2D and C-A (concentrationasymmetry) estimators for 79 galaxies with magnitudes between Ks = 17−23 and classify them into three main morphological types (late type, early type and irregulars). Automated and objective classification allows precise error estimation. Simulations and comparisons with seeing-limited (CFHT/Megacam) and space (HST/ACS) data are carried out to evaluate the accuracy of adaptive optics-based observations for morphological purposes. Results. We obtain the first estimate of the distribution of galaxy types at redshift z ∼ 1 as measured from the near infrared at high spatial resolution. We show that galaxy parameters (disk scale length, bulge effective radius, and bulge fraction) can be estimated with a random error lower than 20% for the bulge fraction up to Ks = 19 (AB = 21) and that classification into the three main morphological types can be done up to Ks = 20 (AB = 22) with at least 70% of the identifications correct. We used the known photometric redshifts to obtain a redshift distribution over 2 redshift bins (z < 0.8, 0.8 < z < 1.5) for each morphological type.