arXiv subjects

V. Gonzalez-Perez

Publications and source records attributed to V. Gonzalez-Perez.

40 records · Page 3Linked to original sources

arXiv2012

The WIRCam Deep Survey I: Counts, colours and mass-functions derived from near-infrared imaging in the CFHTLS deep fields

We present a new near-infrared imaging survey in the four CFHTLS deep fields: the WIRCam Deep Survey (WIRDS). WIRDS comprises extremely deep, high quality (FWHM ~0.6") J, H and K imaging covering a total effective area of 2.1 deg^2 and reaching AB 50% completeness limits of ~24.5. We combine our images with the CFHTLS to create a unique eight-band ugrizJHK photometric catalogues in the CFHTLS deep fields; these four separate fields allow us to make a robust estimate of the effect of cosmic variance for all our measurements. We use these catalogues to estimate precise photometric redshifts, galaxy types and stellar masses for a unique sample of ~1.8 million galaxies. Our JHK number counts are consistent with previous studies. We apply the BzK selection to our gzK filter set and find that the star forming BzK selection successfully selects 76% of star-forming galaxies in the redshift range 1.4<z<2.5 in our photometric catalogue. The passive BzK selection returns 52% of the passive 1.4<z<2.5 population identified in the photometric catalogue. We present the galaxy stellar mass function as a function of redshift up to z=2 and present fits using double Schechter functions. A mass-dependent evolution of the mass function is seen with the numbers of galaxies with masses of log(M)<10.75 still evolving at z<1, but galaxies of higher mass reaching their present day numbers by z~0.8-1. This is consistent with the present picture of downsizing in galaxy evolution. We compare our results with the predictions of the GALFORM semi-analytical galaxy formation model and find that the simulations provide a relatively successful fit to the observed mass functions at intermediate masses (i.e. 10<log(M)<11). However, the GALFORM results under-predict the mass function at low masses, whilst the fit as a whole degrades beyond redshifts of z~1.2.

astro-ph.CO↗

arXiv2010

Colour gradients within SDSS DR7 galaxies: hints of recent evolution

The evolutionary path followed by a galaxy shapes its internal structure, and, in particular, its internal colour variation. We present a study of the internal colour variation within galaxies from the Seventh Data Release of the Sloan Digital Sky Survey (SDSS DR7). We statistically study the connection between the internal colour variation and global galactic properties, looking for hints of the recent galactic evolution. Considering only galaxies with good photometry and spectral measurements, we define four luminosity-threshold samples within the redshift range 0.01<z<0.17, each containing more than 48000 galaxies. Colour gradients are calculated for these galaxies from the surface brightness measurements provided by the SDSS DR7. Possible systematic effects in their determination have been analysed. We find that, on average, galaxies have redder cores than their external parts. We also find that it is more likely to find steep colour gradients among late-type galaxies. This result holds for a range of classifications based on both morphological and spectral characteristics. In fact, our results relate, on average, steep colour gradients to a higher presence of young stars within a galaxy. Our results also suggest that nuclear activity is a marginal driver for creating steep colour gradients in massive galaxies. We have selected pairs of interacting galaxies, with a separation of 5 arcsec, in projected radius, and a difference in redshift of 100 km/s, finding that they present steeper gradients than the average population, skewed towards bluer cores. Our analysis implies that colour gradients can be useful for selecting galaxies that have suffered a recent (minor) burst of star formation.

astro-ph.CO↗

arXiv2010

Extremely Red Objects in a hierarchical universe

We analyse whether hierarchical formation models based on Lambda cold dark matter cosmology can produce enough massive red galaxies to match observations. For this purpose, we compare with observations the predictions from two published models for the abundance and redshift distribution of Extremely Red Objects (EROs), which are red, massive galaxies observed at z >= 1. One of the models invokes a "superwind" to regulate star formation in massive haloes and the other suppresses cooling through "radio-mode" AGN feedback. The first one underestimates the number counts of EROs by an order of magnitude, whereas the radio-mode AGN feedback model gives excellent agreement with the number counts of EROs and redshift distribution of K-selected galaxies. This study highlights the need to consider AGN feedback in order to understand the formation and evolution of massive galaxies at z >= 1.

astro-ph↗

arXiv2010

Massive, red galaxies in a hierarchical universe I. Counts of Extremely Red Objects and basic properties

We present predictions for the abundance and nature of Extremely Red Objects (EROs) in the Lambda cold dark matter model. EROs are red, massive galaxies observed at z>= 1 and their numbers and properties pose a challenge to hierarchical galaxy formation models. We compare the predictions from two published models, one of which invokes a "superwind" to regulate star formation in massive haloes and the other which suppresses gas cooling in haloes through "radio-mode" AGN feedback. The superwind model underestimates the number counts of EROs by an order of magnitude, whereas the radio-mode AGN feedback model gives excellent agreement with the number counts and redshift distribution of EROs. In the AGN feedback model the ERO population is dominated by old, passively evolving galaxies, whereas observations favour an equal split between old galaxies and dusty starbursts. Also, the model predicts a more extended redshift distribution of passive galaxies than is observed. These comparisons suggest that star formation may be quenched too efficiently in this model.

astro-ph↗