Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userZFOURGE: Using Composite Spectral Energy Distributions to Characterize Galaxy Populations at 1<z<4
164
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We investigate the properties of galaxies as they shut off star formation over the 4 billion years surrounding peak cosmic star formation. To do this we categorize $sim7000$ galaxies from $1<z<4$ into $90$ groups based on the shape of their spectral energy distributions (SEDs) and build composite SEDs with $Rsim 50$ resolution. These composite SEDs show a variety of spectral shapes and also show trends in parameters such as color, mass, star formation rate, and emission line equivalent width. Using emission line equivalent widths and strength of the 4000AA break, $D(4000)$, we categorize the composite SEDs into five classes: extreme emission line, star-forming, transitioning, post-starburst, and quiescent galaxies. The transitioning population of galaxies show modest H$alpha$ emission ($EW_{rm REST}sim40$AA) compared to more typical star-forming composite SEDs at $log_{10}(M/M_odot)sim10.5$ ($EW_{rm REST}sim80$AA). Together with their smaller sizes (3 kpc vs. 4 kpc) and higher Sersic indices (2.7 vs. 1.5), this indicates that morphological changes initiate before the cessation of star formation. The transitional group shows a strong increase of over one dex in number density from $zsim3$ to $zsim1$, similar to the growth in the quiescent population, while post-starburst galaxies become rarer at $zlesssim1.5$. We calculate average quenching timescales of 1.6 Gyr at $zsim1.5$ and 0.9 Gyr at $zsim2.5$ and conclude that a fast quenching mechanism producing post-starbursts dominated the quenching of galaxies at early times, while a slower process has become more common since $zsim2$.
rate research
Read More
We present a study of the infrared properties for a sample of seven spectroscopically confirmed submillimeter galaxies at $z>$4.0. By combining ground-based near-infrared, Spitzer IRAC and MIPS, Herschel SPIRE, and ground-based submillimeter/millimeter photometry, we construct their Spectral Energy Distributions (SED) and a composite model to fit the SEDs. The model includes a stellar emission component at $lambda_{rm rest} <$ 3.5$ mu$m; a hot dust component peaking at $lambda_{rest} sim$ 5$,mu$m; and cold dust component which becomes significant for $lambda_{rm rest} >$ 50$,mu$m. Six objects in the sample are detected at 250 and 350$ mu$m. The dust temperatures for the sources in this sample are in the range of 40$-$80 K, and their $L_{rm FIR}$ $sim$ 10$^{13}$ L$_{odot}$ qualifies them as Hyper$-$Luminous Infrared Galaxies (HyperLIRGs). The mean FIR-radio index for this sample is around $< q > = 2.2$ indicating no radio excess in their radio emission. Most sources in the sample have 24$ mu$m detections corresponding to a rest-frame 4.5$ mu$m luminosity of Log$_{10}$(L$_{4.5}$ / L$_{odot}$) = 11 $sim$ 11.5. Their L$_{rm 4.5}$/$L_{rm FIR}$ ratios are very similar to those of starburst dominated submillimeter galaxies at $z sim$ 2. The $L_{rm CO}-L_{rm FIR}$ relation for this sample is consistent with that determined for local ULIRGs and SMGs at $z sim$ 2. We conclude that submillimeter galaxies at $z >$ 4 are hotter and more luminous in the FIR, but otherwise very similar to those at $z sim$ 2. None of these sources show any sign of the strong QSO phase being triggered.
The brightest events in a time series of cosmological transients obey an observation time dependence which is often overlooked. This dependence can be exploited to probe the global properties of electromagnetic and gravitational wave transients (Howell et al. 2007a, Coward & Burman 2005). We describe a new relation based on a peak flux--observation time distribution and show that it is invariant to the luminosity distribution of the sources (Howell et al. 2007b). Applying this relation, in combination with a new data analysis filter, to emph{Swift} gamma-ray burst data, we demonstrate that it can constrain their rate density.
We report the likely identification of a substantial population of massive M~10^11M_Sun galaxies at z~4 with suppressed star formation rates (SFRs), selected on rest-frame optical to near-IR colors from the FourStar Galaxy Evolution Survey. The observed spectral energy distributions show pronounced breaks, sampled by a set of near-IR medium-bandwidth filters, resulting in tightly constrained photometric redshifts. Fitting stellar population models suggests large Balmer/4000AA breaks, relatively old stellar populations, large stellar masses and low SFRs, with a median specific SFR of 2.9+/-1.8 x 10^-11/yr. Ultradeep Herschel/PACS 100micron, 160micron and Spitzer/MIPS 24micron data reveal no dust-obscured SFR activity for 15/19 (79%) galaxies. Two far-IR detected galaxies are obscured QSOs. Stacking the far-IR undetected galaxies yields no detection, consistent with the SED fit, indicating independently that the average specific SFR is at least 10x smaller than of typical star-forming galaxies at z~4. Assuming all far-IR undetected galaxies are indeed quiescent, the volume density is 1.8+/-0.7 x 10^-5Mpc^-3 to a limit of log10M/M_Sun>10.6, which is 10x and 80x lower than at z = 2 and z = 0.1. They comprise a remarkably high fraction (~35%) of z~4 massive galaxies, suggesting that suppression of star formation was efficient even at very high redshift. Given the average stellar age of 0.8Gyr and stellar mass of 0.8x10^11M_Sun, the galaxies likely started forming stars before z =5, with SFRs well in excess of 100M_Sun/yr, far exceeding that of similarly abundant UV-bright galaxies at z>4. This suggests that most of the star-formation in the progenitors of quiescent z~4 galaxies was obscured by dust.
We present observed mid-infrared and optical colors and composite spectral energy distributions (SEDs) of type 1 (broad-line) and 2 (narrow-line) quasars selected from Sloan Digital Sky Survey (SDSS) spectroscopy. A significant fraction of powerful quasars are obscured by dust, and are difficult to detect in optical photometric or spectroscopic surveys. However these may be more easily identified on the basis of mid-infrared (MIR) colors and SEDs. Using samples of SDSS type 1 type 2 matched in redshift and [OIII] luminosity, we produce composite rest-frame 0.2-15 micron SEDs based on SDSS, UKIDSS, and Wide-Field Infrared Survey Explorer (WISE) photometry and perform model fits using simple galaxy and quasar SED templates. The SEDs of type 1 and 2 quasars are remarkably similar, with the differences explained primarily by the extinction of the quasar component in the type 2 systems. For both types of quasar, the flux of the AGN relative to the host galaxy increases with AGN luminosity (L_[OIII]) and redder observed MIR color, but we find only weak dependencies of the composite SEDs on mechanical jet power as determined through radio luminosity. We conclude that luminous quasars can be effectively selected using simple MIR color criteria similar to those identified previously (W1-W2 > 0.7 [Vega]), although these criteria miss many heavily obscured objects. Obscured quasars can be further identified based on optical-IR colors (for example, (u-W3 [AB]) > 1.4(W1-W2 [Vega])+3.2). These results illustrate the power of large statistical studies of obscured quasars selected on the basis of mid-IR and optical photometry.
We select a sample of radio galaxies at high redshifts (z>~1) in the COSMOS field, by cross-matching optical/infrared images with the FIRST radio data. The aim of this study is to explore the high-z radio-loud (RL) AGN population at much lower luminosities than the classical samples of distant radio sources and similar to those of the local population of radio galaxies. The wide multiwavelength coverage provided by the COSMOS survey allows us to derive their Spectral Energy Distributions (SEDs). The SED modeling with stellar and dust components (with our code 2SPD) returns several important quantities associated with the AGN and host properties. The final sample consists of 74 RL AGN, which extends the sample previously selected by Chiaberge et al. (2009) and studied by Baldi et al. (2013). The resulting photometric redshifts range from z~0.7 to 3. The sample mostly includes compact radio sources, but also 21 FRIIs; the radio power distribution of the sample at 1.4 GHz covers ~10^(31.5)-10^(34.3) ergsHz. The stellar mass of the hosts ranges ~10^(10)-10^(11.5) M_{sun}. The SEDs are dominated by the contribution from an old stellar population for most of the sources. UV and mid-IR (MIR) excesses are observed for half of the sample. The dust luminosities are in the range L_(dust) ~10^(43)-10^(45.5) erg/s (T ~350-1200 K). UV luminosities at 2000 A ranges ~10^(41.5)-10^(45.5) erg/s. UV emission is significantly correlated with both IR and radio luminosities, the former being the stronger link. However, the origin of UV and dust emission, whether it is produced by the AGN of by star formation, is still unclear. Our results show that this RL AGN population at high redshifts displays a wide variety of properties from possible quasars at the highest luminosities, to low-luminosity old galaxies, similarly to the local FRI-FRII dichotomy.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
