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Register a new userHELP: modelling the spectral energy distributions of Herschel detected galaxies in the ELAIS N1 field
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Katarzyna Malek Mrs.
Publication date
2018
fields
Physics
and research's language is
English
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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.
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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 gather infrared (IR) photometric data from 8 to 500 microns (Spitzer, WISE, IRAS and Herschel) for all of the HRS galaxies. Draine & Li (2007) models are fit to the data from which the stellar contribution has been carefully removed. We find that our photometric coverage is sufficient to constrain all of the models parameters and that a strong constraint on the 20-60 microns range is mandatory to estimate the relative contribution of the photo-dissociation regions to the IR SED. The SED models tend to systematically under-estimate the observed 500 microns flux densities, especially for low mass systems. We provide the output parameters for all of the galaxies: the minimum intensity of the interstellar radiation field (ISRF), the fraction of PAH, the relative contribution of PDR and evolved stellar population to the dust heating, the $M_{dust}$ and the $L_{IR}$. For a subsample of gas-rich galaxies, we analyze the relations between these parameters and the integrated properties of galaxies, such as $M_*$, SFR, metallicity, H$alpha$ and H-band surface brightness, and the FUV attenuation. A good correlation between the fraction of PAH and the metallicity is found implying a weakening of the PAH emission in galaxies with low metallicities. The intensity of the IRSF and the H-band and H$alpha$ surface brightnesses are correlated, suggesting that the diffuse dust component is heated by both the young stars in star forming regions and the diffuse evolved population. We use these results to provide a new set of IR templates calibrated with Herschel observations on nearby galaxies and a mean SED template to provide the z=0 reference for cosmological studies. For the same purpose, we put our sample on the SFR-$M_*$ diagram. The templates are compared to the most popular IR SED libraries, enlightening a large discrepancy between all of them in the 20-100 microns range.
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.
In this paper we present a wide-area 610 MHz survey of the ELAIS,N1 field with the GMRT, covering an area of 12.8 deg$^2$ at a resolution of 6 arcsec and with an rms noise of $sim 40$ $mu$Jy beam$^{-1}$. This is equivalent to $sim 20$ $mu$Jy beam$^{-1}$ rms noise at 1.4 GHz for a spectral index of $-0.75$. The primary goal of the survey was to study the polarised sky at sub-mJy flux densities at $<$ GHz frequencies. In addition, a range of other science goals, such as investigations in to the nature of the low-frequency $mu$Jy source populations and alignments of radio jets. A total of 6,400 sources were found in this region, the vast majority of them compact. The sample jointly detected by GMRT at 610 MHz and by VLA FIRST at 1.4,GHz has a median spectral index of $-0.85 pm 0.05$ and a median 610 MHz flux density of 4.5 mJy. This region has a wealth of ancillary data which is useful to characterize the detected sources. The multi-wavelength cross matching resulted optical/IR counterparts to $sim 90$ per~cent of the radio sources, with a significant fraction having at least photometric redshift. Due to the improved sensitivity of this survey over preceding ones, we have discovered six giant radio sources (GRS), with three of them at $z sim 1$ or higher. This implies that the population of GRS may be more abundant and common than known to date and if true this has implications for the luminosity function and the evolution of radio sources. We have also identified several candidate extended relic sources.
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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