IDENTIFICAÇÃO E ESTUDO DE FONTES DE RÁDIO NO STRIPE82 DO SOUTHERN PHOTOMETRIC LOCAL UNIVERSE SURVEY

Abstract

Galaxies hosting active galactic nuclei (AGNs) play an important role in the evolution of galaxies. These AGNs are powered by the accretion of matter onto a supermassive black hole, which can result in highly energetic and multiwavelength emission that is unique to this class of galaxies. A subset of the AGN population consists of so-called radio-loud AGN, i.e., they have a strong excess of radio (synchrotron) emission compared to their optical output. This class, which consists mostly of radio galaxies and radio quasars, are particularly important because of the feedback mechanisms that result as their expanding radio jets interact with the surrounding gas on kpc to Mpc scales. These radio AGN are thus a key population for, e.g., studying the triggering of large-scale jets in galaxies and the outflow and heating mechanisms associated with jets, for identifying dense environments such as groups and clusters of galaxies, or for locating massive galaxies and supermassive black holes especially at high redshifts. However, radio AGN are fairly rare in the sky, and, moreover, they are difficult to find. This is because radio surveys do not provide direct information on the distances of the sources, making identification of their host galaxies a difficult process. In the Northern hemisphere, this problem was largely overcome by combining wide-field radio surveys such as the NVSS and FIRST with the SDSS optical survey. In the Southern hemisphere, there is no equivalent of the SDSS spectroscopic survey, hampering the identification of new radio sources. The Southern Photometric Local Universe Survey (S-PLUS) has the potential to change this situation. This brazilian-led 12-band photometric survey is imaging thousands of square degrees delivering photometric redshifts and other information for millions of galaxies down to r = 21 mag. In this dissertation, we carry out a pilot project of identifying radio sources using S-PLUS in the SDSS Stripe82 region. We used a mixed-method of visual inspection and automatic identification for 4186 radio sources from (Hodge et al.,2011) and were able to find optical counterparts for 1316 of them. Sources were divided, in terms of their radio morphology, into five classes: compact, FR1, FR2, extended or uncertain (in case the radio morphology was not clear). In a subsequent step, we used the optical colors, radio luminosities and far-infrared fluxes, and built selection criteria to classify the sources as quasars (QSOs), Active Galaxy Nuclei (AGNs) or Star-Forming Galaxies (SFGs). Our selection resulted in 35 new quasar candidates and 15 new radio AGNs candidates. We were able to classify 159 sources as SFGs, 72 of them with no previous identification in spectroscopic catalogs. We also demonstrated the power of using radio surveys to determine star formation rates in normal (i.e., non-AGN) galaxies found in S-PLUS. This will be a valuable addition to the spectral properties that can be derived from the S-PLUS photometry (such as photometric redshift, optical morphology, stellar mass and age). Finally, this study is also valuable for the identification of radio sources that are not detected in S-PLUS. These sources will include highly obscured radio sources and very distant AGN (quasars and radio galaxies) that will be a very interesting class of sources worthy of follow-up with deeper imaging or spectroscopy. This work shows that the combination of radio surveys and future releases of S-PLUS will be a powerful tool for exploring the radio-bright extragalactic sky. Keywords: Galaxies hosting active galactic nuclei (AGNs) play an important role in the evolution of galaxies. These AGNs are powered by the accretion of matter onto a supermassive black hole, which can result in highly energetic and multiwavelength emission that is unique to this class of galaxies. A subset of the AGN population consists of so-called radio-loud AGN, i.e., they have a strong excess of radio (synchrotron) emission compared to their optical output. This class, which consists mostly of radio galaxies and radio quasars, are particularly important because of the feedback mechanisms that result as their expanding radio jets interact with the surrounding gas on kpc to Mpc scales. These radio AGN are thus a key population for, e.g., studying the triggering of large-scale jets in galaxies and the outflow and heating mechanisms associated with jets, for identifying dense environments such as groups and clusters of galaxies, or for locating massive galaxies and supermassive black holes especially at high redshifts. However, radio AGN are fairly rare in the sky, and, moreover, they are difficult to find. This is because radio surveys do not provide direct information on the distances of the sources, making identification of their host galaxies a difficult process. In the Northern hemisphere, this problem was largely overcome by combining wide-field radio surveys such as the NVSS and FIRST with the SDSS optical survey. In the Southern hemisphere, there is no equivalent of the SDSS spectroscopic survey, hampering the identification of new radio sources. The Southern Photometric Local Universe Survey (S-PLUS) has the potential to change this situation. This brazilian-led 12-band photometric survey is imaging thousands of square degrees delivering photometric redshifts and other information for millions of galaxies down to r = 21 mag. In this dissertation, we carry out a pilot project of identifying radio sources using S-PLUS in the SDSS Stripe82 region. We used a mixed-method of visual inspection and automatic identification for 4186 radio sources from (Hodge et al.,2011) and were able to find optical counterparts for 1316 of them. Sources were divided, in terms of their radio morphology, into five classes: compact, FR1, FR2, extended or uncertain (in case the radio morphology was not clear). In a subsequent step, we used the optical colors, radio luminosities and far-infrared fluxes, and built selection criteria to classify the sources as quasars (QSOs), Active Galaxy Nuclei (AGNs) or Star-Forming Galaxies (SFGs). Our selection resulted in 35 new quasar candidates and 15 new radio AGNs candidates. We were able to classify 159 sources as SFGs, 72 of them with no previous identification in spectroscopic catalogs. We also demonstrated the power of using radio surveys to determine star formation rates in normal (i.e., non-AGN) galaxies found in S-PLUS. This will be a valuable addition to the spectral properties that can be derived from the S-PLUS photometry (such as photometric redshift, optical morphology, stellar mass and age). Finally, this study is also valuable for the identification of radio sources that are not detected in S-PLUS. These sources will include highly obscured radio sources and very distant AGN (quasars and radio galaxies) that will be a very interesting class of sources worthy of follow-up with deeper imaging or spectroscopy. This work shows that the combination of radio surveys and future releases of S-PLUS will be a powerful tool for exploring the radio-bright extragalactic sky.