اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe LOFAR window on star-forming galaxies and AGN - curved radio SEDs and IR-radio correlation at $0 < z < 2.5$
88
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present a study of the low-frequency radio properties of star forming (SF) galaxies and active galactic nuclei (AGN) up to redshift $z=2.5$. The new spectral window probed by the Low Frequency Array (LOFAR) allows us to reconstruct the radio continuum emission from 150 MHz to 1.4 GHz to an unprecedented depth for a radio-selected sample of $1542$ galaxies in $sim 7~ rm{deg}^2$ of the LOFAR Bootes field. Using the extensive multi-wavelength dataset available in Bootes and detailed modelling of the FIR to UV spectral energy distribution (SED), we are able to separate the star-formation (N=758) and the AGN (N=784) dominated populations. We study the shape of the radio SEDs and their evolution across cosmic time and find significant differences in the spectral curvature between the SF galaxy and AGN populations. While the radio spectra of SF galaxies exhibit a weak but statistically significant flattening, AGN SEDs show a clear trend to become steeper towards lower frequencies. No evolution of the spectral curvature as a function of redshift is found for SF galaxies or AGN. We investigate the redshift evolution of the infrared-radio correlation (IRC) for SF galaxies and find that the ratio of total infrared to 1.4 GHz radio luminosities decreases with increasing redshift: $ q_{rm 1.4GHz} = (2.45 pm 0.04) times (1+z)^{-0.15 pm 0.03} $. Similarly, $q_{rm 150MHz}$ shows a redshift evolution following $ q_{rm 150GHz} = (1.72 pm 0.04) times (1+z)^{-0.22 pm 0.05}$. Calibration of the 150 MHz radio luminosity as a star formation rate tracer suggests that a single power-law extrapolation from $q_{rm 1.4GHz}$ is not an accurate approximation at all redshifts.
قيم البحث
اقرأ أيضاً
We report the identification of radio (1.4 and 3 GHz) and mid-infrared, far-infrared, and sub-mm (24-850$mu$m) emission at the position of one of 41 UV-bright ($mathrm{M_{UV}^{}}lesssim-21.25$) $zsimeq6.6-6.9$ Lyman-break galaxy candidates in the 1.5
deg$^2$ COSMOS field. This source, COS-87259, exhibits a sharp flux discontinuity (factor $>$3) between two narrow/intermediate bands at 9450 $mathring{A}$ and 9700 $mathring{A}$ and is undetected in all nine bands blueward of 9600 $mathring{A}$, as expected from a Lyman-alpha break at $zsimeq6.8$. The full multi-wavelength (X-ray through radio) data of COS-87529 can be self-consistently explained by a very massive (M$_{ast}=10^{10.8}$ M$_{odot}$) and extremely red (rest-UV slope $beta=-0.59$) $zsimeq6.8$ galaxy with hyperluminous infrared emission (L$_{mathrm{IR}}=10^{13.6}$ L$_{odot}$) powered by both an intense burst of highly-obscured star formation (SFR$approx$1800 M$_{odot}$ yr$^{-1}$) and an obscured ($tau_{mathrm{9.7mu m}}=7.7pm2.5$) radio-loud (L$_{mathrm{1.4 GHz}}sim10^{25.5}$ W Hz$^{-1}$) AGN. The radio emission is compact (1.04$pm$0.12 arcsec) and exhibits an ultra-steep spectrum between 1.4-3 GHz ($alpha=-2.06^{+0.27}_{-0.25}$) with evidence of spectral flattening at lower frequencies, consistent with known $z>4$ radio galaxies. We also demonstrate that COS-87259 may reside in a significant (11$times$) galaxy overdensity at $zsimeq6.6-6.9$, as common for systems hosting radio-loud AGN. Nonetheless, a spectroscopic redshift will ultimately be required to establish the true nature of COS-87259 as we cannot yet completely rule out low-redshift solutions. If confirmed to lie at $zsimeq6.8$, the properties of COS-87259 would be consistent with a picture wherein AGN and highly-obscured star formation activity are fairly common among very massive (M$_{ast}>10^{10}$ M$_{odot}$) reionization-era galaxies.
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 t
heir 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.
We examine the behaviour of the infrared-radio correlation (IRRC) over the range $0<z<6$ using new, highly sensitive 3GHz observations with the Karl G. Jansky Very Large Array (VLA) and infrared data from the Herschel Space Observatory in the 2deg$^{
2}$ COSMOS field. We distinguish between objects where emission is believed to arise solely from star-formation, and those where an active galactic nucleus (AGN) is thought to be present. We account for non-detections in the radio or in the infrared using a doubly-censored survival analysis. We find that the IRRC of star-forming galaxies, quantified by the infrared-to-1.4GHz radio luminosity ratio ($q_{rm TIR}$), decreases with increasing redshift: $q_{rm TIR}(z)=(2.88pm0.03)(1+z)^{-0.19pm0.01}$. Moderate-to-high radiative luminosity AGN do not follow the same $q_{rm TIR}$$(z)$ trend, having a lower normalisation and steeper decrease with redshift. We cannot rule out the possibility that unidentified AGN contributions only to the radio regime may be steepening the observed $q_{rm TIR}(z)$ trend of the star-forming population. An increasing fractional contribution to the observed 3GHz flux by free-free emission of star-forming galaxies may also affect the derived evolution. However, we find that the standard (M82-based) assumption of the typical radio spectral energy distribution (SED) for star-forming galaxies is inconsistent with our results. This suggests a more complex shape of the typical radio SED for star-forming galaxies, and that imperfect $K$ corrections in the radio may govern the derived redshift trend of $q_{rm TIR}$. Lastly, we present a redshift-dependent relation between rest-frame 1.4GHz radio luminosity and star formation rate taking the derived redshift trend into account.
We present a study of the gas kinematics of star-forming galaxies associated with protocluster 4C 23.56 at $z=2.49$ using $0.4$ resolution CO (4-3) data taken with ALMA. Eleven H$alpha$ emitters (HAEs) are detected in CO (4-3), including six HAEs tha
t were previously detected in CO (3-2) at a coarser angular resolution. The detections in both CO lines are broadly consistent in the line widths and the redshifts, confirming both detections. With an increase in the number of spectroscopic redshifts, we confirm that the protocluster is composed of two merging groups with a total halo mass of $log{(M_{rm cl}/M_{odot})} =13.4-13.6$, suggesting that the protocluster would evolve into a Virgo-like cluster ($>10^{14} M_{odot}$). We compare the CO line widths and the CO luminosities with galaxies in other (proto)clusters ($n_{rm gal}=91$) and general fields ($n_{rm gal}=80$) from other studies. The 4C23.56 protocluster galaxies have CO line widths and luminosities comparable to other protocluster galaxies on average. On the other hand, the CO line widths are on average broader by $approx50%$ compared to field galaxies, while the median CO luminosities are similar. The broader line widths can be attributed to both effects of unresolved gas-rich mergers and/or compact gas distribution, which is supported by our limited but decent angular resolution observations and the size estimate of three galaxies. Based on these results, we argue that gas-rich mergers may play a role in the retention of the specific angular momentum to a value similar to that of field populations during cluster assembly, though we need to verify this with a larger number of samples.
We compare the kinetic energy and momentum injection rates from intense star formation, bolometric AGN radiation, and radio jets with the kinetic energy and momentum observed in the warm ionized gas in 24 powerful radio galaxies at z~2. These galaxie
s are amongst our best candidates for being massive galaxies near the end of their active formation period, when intense star formation, quasar activity, and powerful radio jets all co-exist. All galaxies have VLT/SINFONI imaging spectroscopy of the rest-frame optical line emission, showing emission-line regions with large velocity offsets (up to 1500 km/s) and line widths (typically 800-1000 km/s) consistent with very turbulent, often outflowing gas. As part of the HeRGE sample, they also have FIR estimates of the star formation and quasar activity obtained with Herschel/PACS and SPIRE, which enables us to measure the relative energy and momentum release from each of the three main sources of feedback in massive, star-forming AGN host galaxies during their most rapid formation phase. We find that star formation falls short by factors 10-1000 of providing the energy and momentum necessary to power the observed gas kinematics. The obscured quasars in the nuclei of these galaxies provide enough energy and momentum in about half of the sample, however, only if these are transfered to the gas relatively efficiently. We compare with theoretical and observational constraints on the efficiency of the energy and momentum transfer from jet and AGN radiation, which advocates that the radio jet is the main driver of the gas kinematics.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
