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Register a new userThe study of the angular and spatial distribution of radio selected AGNs and star-forming galaxies in the ELAIS N1 field
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The cosmic evolution of bias of different source populations with underlying dark matter density field in post reionization era can shed light on large scale structures. Studying the angular and spatial distribution of different compact sources using deep radio catalogue at low-frequency is essential to understand the matter distribution of the present Universe. Here, we investigate the relationship of luminous matter with their host dark matter haloes by measuring the angular and spatial clustering of sources (two-point statistics), using deep radio observation of ELAIS N1 (EN1) field with upgraded Giant Metrewave Radio Telescope (uGMRT) at 300-500 MHz. We also analyze the 612 MHz GMRT archival data of the same field to understand the cosmic evolution of clustering of different source populations. We classify the sources as star-forming galaxies (SFGs) and active galactic nuclei (AGN) based on their radio luminosity. We find that the spatial clustering length and bias to the dark matter density field of SFGs are smaller than AGNs at both frequencies. This proves that AGNs are mainly hosted by massive haloes and hence strongly clustered. However, a small decrease in the bias for both kind of sources at higher frequency indicates that we are most likely tracing the faint objects residing in less massive haloes at higher frequencies. Our results are in excellent agreement with previous findings at radio and multi-frequency surveys. However, comparison with SKADS simulation suggests that the halo mass for different populations used in the simulation is systematically lower. This work quantifies the spatial distribution of extragalactic compact objects in EN1 field and bridges the gap between shallow and deep surveys.
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Dark matter haloes in which galaxies reside are likely to have a significant impact on their evolution. We investigate the link between dark matter haloes and their constituent galaxies by measuring the angular two-point correlation function of radio sources, using recently released 3 GHz imaging over $sim 2 mathrm{deg}^2$ of the COSMOS field. We split the radio source population into Star Forming Galaxies (SFGs) and Active Galactic Nuclei (AGN), and further separate the AGN into radiatively efficient and inefficient accreters. Restricting our analysis to $z<1$, we find SFGs have a bias, $b = 1.5 ^{+0.1}_{-0.2}$, at a median redshift of $z=0.62$. On the other hand, AGN are significantly more strongly clustered with $b = 2.1pm 0.2$ at a median redshift of 0.7. This supports the idea that AGN are hosted by more massive haloes than SFGs. We also find low-accretion rate AGN are more clustered ($b = 2.9 pm 0.3$) than high-accretion rate AGN ($b = 1.8^{+0.4}_{-0.5}$) at the same redshift ($z sim 0.7$), suggesting that low-accretion rate AGN reside in higher mass haloes. This supports previous evidence that the relatively hot gas that inhabits the most massive haloes is unable to be easily accreted by the central AGN, causing them to be inefficient. We also find evidence that low-accretion rate AGN appear to reside in halo masses of $M_{h} sim 3-4 times 10^{13}h^{-1}$M$_{odot}$ at all redshifts. On the other hand, the efficient accreters reside in haloes of $M_{h} sim 1-2 times 10^{13}h^{-1}$M$_{odot}$ at low redshift but can reside in relatively lower mass haloes at higher redshifts. This could be due to the increased prevalence of cold gas in lower mass haloes at $z ge 1$ compared to $z<1$.
We report the discovery of a remnant radio AGN J1615+5452 in the field of ELAIS-N1. GMRT continuum observations at 150, 325 and 610 MHz combined with archival data from the 1.4 GHz NVSS survey were used to derive the radio spectrum of the source. At a redshift $z sim$ 0.33, J1615+5452 has a linear size of $sim$ 100 kpc and spectral indices ranging between $alpha^{1400}_{610} < -1.5$ and $alpha^{325}_{150} = -0.61 pm 0.12$. While the source has a diffuse radio emission at low frequencies, we do not find evidence of core, jets or hotspots in the 1.4,GHz VLA data of $sim 5$ arcsec angular resolution. Such morphological properties coupled with a curved radio spectrum suggest that the AGN fueling mechanisms undergo a shortage of energy supply which is typical of a dying radio AGN. This is consistent with the observed steep curvature in the spectrum $Deltaalpha approx -1$, the estimated synchrotron age of $t_{rm s}=76.0^{+7.4}_{-8.7}$ Myr and a $t_{rm off}/t_{rm s}$ ratio of $sim 0.3$.
We present the clustering properties of a complete sample of 968 radio sources detected at 1.4 GHz by the VLA-COSMOS survey with radio fluxes brighter than 0.15 mJy. 92% have redshift determinations from the Laigle et al. (2016) catalogue. Based on their radio-luminosity, these objects have been divided into two populations of 644 AGN and 247 star-forming galaxies. By fixing the slope of the auto-correlation function to gamma=2, we find r_0=11.7^{+1.0}_{-1.1} Mpc for the clustering length of the whole sample, while r_0=11.2^{+2.5}_{-3.3} Mpc and r_0=7.8^{+1.6}_{-2.1} Mpc (r_0=6.8^{+1.4}_{-1.8} Mpc if we restrict our analysis to z<0.9) are respectively obtained for AGN and star-forming galaxies. These values correspond to minimum masses for dark matter haloes of M_min=10^[13.6^{+0.3}_{-0.6}] M_sun for radio-selected AGN and M_min=10^[13.1^{+0.4}_{-1.6}] M_sun for radio-emitting star-forming galaxies (M_min=10^[12.7^{+0.7}_{-2.2}] M_sun for z<0.9). Comparisons with previous works imply an independence of the clustering properties of the AGN population with respect to both radio luminosity and redshift. We also investigate the relationship between dark and luminous matter in both populations. We obtain <M*>/M_halo<~10^{-2.7} for AGN, and <M*>/M_halo<~10^{-2.4} in the case of star-forming galaxies. Furthermore, if we restrict to z<~0.9 star-forming galaxies, we derive <M*>/M_halo<~10^{-2.1}, result which clearly indicates the cosmic process of stellar build-up as one moves towards the more local universe. Comparisons between the observed space density of radio-selected AGN and that of dark matter haloes shows that about one in two haloes is associated with a black hole in its radio-active phase. This suggests that the radio-active phase is a recurrent phenomenon.
The HELP project focuses on the data from ESAs Herschel mission, which covered over 1300$deg^2$ and is preparing to publish a multi-wavelength catalogue of millions of objects. Our main goal is to find the best approach to simultaneously fitting SEDs of millions of galaxies across a wide redshift range to obtain homogeneous estimates of the main physical parameters of detected IR galaxies. We perform SED fitting on the UV/NIR to FIR emission of 42 047 galaxies from the pilot HELP field: ELAIS N1. We use the latest release of CIGALE, a galaxy SED fitting code relying on energy balance, to deliver the main physical parameters such as $M_{star}$, SFR, and $L_{dust}$. We implement additional quality criteria to the fits by calculating $chi^2$ values for the stellar and dust part of the spectra independently. These criteria allow us to identify the best fits and to identify peculiar galaxies. We perform the SED fitting by assuming three different dust attenuation laws separately allowing us to test the impact of the assumed law on estimated physical parameters. We implemented two additional quality value checks for the SED fitting method based on $M_{star}$ estimation and energy budget. This method allows us to identify possible objects with incorrect matching in the catalogue and peculiar galaxies; we found 351 possible candidates of lensed galaxies using two complementary $chi^2$s criteria (stellar and IR) and $z_{phot}$ calculated for the IR part of the spectrum only. We find that the attenuation law has an important impact on the $M_{star}$ estimate (on average leading to disparities of a factor of two). We derive the relation between $M_{star}$ estimates obtained by different attenuation laws and we find the best recipe for our sample. We also make independent estimates of the total $L_{dust}$ parameter from stellar emission by fitting the galaxies with and without IR data separately.
We study the cosmic evolution of radio sources out to $z simeq 1.5$ using a GMRT 610 MHz survey covering $sim$1.86 deg$^2$ of the ELAIS N1 field with a minimum/median rms noise 7.1/19.5,$mu$Jy / beam and an angular resolution of 6,arcsec. We classify sources as star forming galaxies (SFGs), radio-quiet (RQ) and radio-loud (RL) Active Galactic Nuclei (AGN) using a combination of multi-wavelength diagnostics and find evidence in support of the radio emission in SFGs and RQ AGN arising from star formation, rather than AGN-related processes. At high luminosities, however, both SFGs and RQ AGN display a radio excess when comparing radio and infrared star formation rates. The vast majority of our sample lie along the $rm{SFR - M_{star}}$ main sequence at all redshifts when using infrared star formation rates. We derive the 610 MHz radio luminosity function for the total AGN population, constraining its evolution via continuous models of pure density and pure luminosity evolution with $rm{Phi^{star},propto,(,1+,z)^{(2.25pm0.38)-(0.63pm0.35)z}}$ and $rm{L_{610,MHz},propto,(,1+,z)^{(3.45pm0.53)-(0.55pm0.29)z}}$ respectively. For our RQ and RL AGN, we find a fairly mild evolution with redshift best fitted by pure luminosity evolution with $rm{L_{610,MHz},propto,(,1+,z)^{(2.81pm0.43)-(0.57pm0.30)z}}$ for RQ AGN and $rm{L_{610,MHz},propto,(,1+,z)^{(3.58pm0.54)-(0.56pm0.29)z}}$ for RL AGN. The 610 MHz radio AGN population thus comprises two differently evolving populations whose radio emission is mostly SF-driven or AGN-driven respectively.
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