arXiv subjects

Jose Afonso

Publications and source records attributed to Jose Afonso.

41 records · Page 3Linked to original sources

arXiv2010

A multi-wavelength approach to the properties of Extremely Red Galaxy populations: I - Contribution to the Star Formation Rate density and AGN content

We present a multi-wavelength analysis of the properties of Extremely Red Galaxy (ERG) populations, selected in the GOODS-South/Chandra Deep Field South field. By using all the photometric and spectroscopic information available on large deep samples of EROs (645 sources), IEROs (294 sources), and DRGs (350 sources), we derive redshift distributions, identify AGN powered and Star-formation powered galaxies, and, using the radio observations of this field, estimate robust (AGN- and dust-unbiased) Star Formation Rate Densities (SFRD) for these populations. We also investigate the properties of "pure" (galaxies that conform to only one of the three ERG criteria considered) and "combined" (galaxies that verify all three criteria) sub-populations. Overall, a large number of AGN are identified (up to ~30%, based on X-rays, and mid-infrared criteria), the majority of which are type-2 (obscured) objects. Among ERGs with no evidence for AGN activity, we identify sub-populations covering a wide range of average star-formation rates, from below 10 Mo/yr to as high as 200 Mo/yr. Applying a redshift separation (1<z<2 and 2<z<3) we find significant evolution (an increase of a factor of 2 or higher) of SFRD for EROs and DRGs, while none is observed for IEROs. The former populations can contribute more than 20\% to the global SFRD at 2<z<3. The emission from AGN activity is typically not strong in the ERG population, with AGN increasing the average radio luminosity of ERG sub-populations by, nominally, less than 20%. AGN are common, however, and, if no discrimination is attempted, this could significantly increase the SFRD estimate (by over 100% in some cases). Thus, and while the contribution of star forming processes to the radio luminosity in galaxies with AGN remains uncertain, a comprehensive identification of AGN in these populations is necessary to obtain meaningful results.

astro-ph.CO↗

arXiv2007

Evidence that FeLoBALs may signify the transition between an ultraluminous infrared galaxy and a quasar

We present mid/far-infrared photometry of nine FeLoBAL QSOs, taken using the Spitzer space telescope. All nine objects are extremely bright in the infrared, with rest-frame 1-1000 micron luminosities comparable to those of Ultraluminous Infrared Galaxies. Furthermore, a significant fraction of the infrared emission from many, and possibly all of the sample is likely to arise from star formation, with star formation rates of order several hundred solar masses per year. We combine these results with previous work to propose that FeLoBALs mark galaxies and QSOs in which an extremely luminous starburst is approaching its end, and in which a rapidly accreting supermassive black hole is in the last stages of casting off its dust cocoon. FeLoBAL signatures in high redshift QSOs and galaxies may thus be an efficient way of selecting sources at a critical point in their evolution.

astro-ph↗

arXiv2006

Deep ATLAS radio observations of the CDFS-SWIRE field

We present the first results from the Australia Telescope Large Area Survey (ATLAS), which consist of deep radio observations of a 3.7 square degree field surrounding the Chandra Deep Field South, largely coincident with the infrared Spitzer Wide-Area Extragalactic (SWIRE) Survey. We also list cross-identifications to infrared and optical photometry data from SWIRE, and ground-based optical spectroscopy. A total of 784 radio components are identified, corresponding to 726 distinct radio sources, nearly all of which are identified with SWIRE sources. Of the radio sources with measured redshifts, most lie in the redshift range 0.5-2, and include both star-forming galaxies and active galactic nuclei (AGN). We identify a rare population of infrared-faint radio sources which are bright at radio wavelengths but are not seen in the available optical, infrared, or X-ray data. Such rare classes of sources can only be discovered in wide, deep surveys such as this.

astro-ph↗

arXiv2004

The Phoenix Deep Survey: Optical and near infrared imaging catalogs

The Phoenix Deep Survey is a multi-wavelength galaxy survey based on deep 1.4 GHz radio imaging (Hopkins et al., 2003). The primary goal of this survey is to investigate the properties of star formation in galaxies and to trace the evolution in those properties to a redshift z=1, covering a significant fraction of the age of the Universe. By compiling a sample of star-forming galaxies based on selection at radio wavelengths we eliminate possible biases due to dust obscuration, a significant issue when selecting objects at optical and ultraviolet wavelengths. In this paper, we present the catalogs and results of deep optical (UBVRI) and near-infrared (Ks) imaging of the deepest region of the existing decimetric radio imaging. The observations and data-processing are summarised and the construction of the optical source catalogs described, together with the details of the identification of candidate optical counterparts to the radio catalogs. Based on our UBVRIKs imaging, photometric redshift estimates for the optical counterparts to the radio detections are explored.

astro-ph↗

arXiv2001

ISO Observations of Star-forming Galaxies

The Infrared Space Observatory (ISO) is used to carry out mid-IR (7 and 15 micron) and far-IR (90 micron) observations of a sample of star-forming sub-mJy radio sources. By selecting the sample at radio wavelengths, one avoids biases due to dust obscuration. It is found that the mid-IR luminosities, covering the PAH features, measure the star formation rate for galaxies with $P_{1.4 GHz} < 10^{23}$ W Hz$^{-1}$. This is further confirmed using the H$α$ luminosities. The far-IR emission is also found to trace the SFR over the whole range of radio and H$α$ luminosities. The implication of the mid-IR measurements in estimating the SFRs from the future infrared space missions (SIRTF and ASTRO-F) is discussed.

astro-ph↗