scholarly journals Observations by GMRT at 323 MHz of radio-loud quasars at z  >  5

2020 ◽  
Vol 641 ◽  
pp. A85
Author(s):  
Yali Shao ◽  
Jeff Wagg ◽  
Ran Wang ◽  
Chris L. Carilli ◽  
Dominik A. Riechers ◽  
...  
Keyword(s):  
Power Law ◽  
Rest Frame ◽  
Low Frequency ◽  
Point Sources ◽  
Radio Continuum ◽  
Spectral Energy ◽  
Synchrotron Emission ◽  
Energy Distributions ◽  
Radio Range ◽  
Wide Range

We present Giant Metrewave Radio Telescope (GMRT) 323 MHz radio continuum observations toward 13 radio-loud quasars at z >  5, sampling the low-frequency synchrotron emission from these objects. Among the 12 targets successfully observed, we detected 10 above 4σ significance, while 2 remain undetected. All of the detected sources appear as point sources. Combined with previous radio continuum detections from the literature, 9 quasars have power-law spectral energy distributions throughout the radio range; for some the flux density drops with increasing frequency while it increases for others. Two of these sources appear to have spectral turnover. For the power-law-like sources, the power-law indices have a positive range between 0.18 and 0.67 and a negative values between −0.90 and −0.27. For the turnover sources, the radio peaks around ∼1 and ∼10 GHz in the rest frame, the optically thin indices are −0.58 and −0.90, and the optically thick indices are 0.50 and 1.20. A magnetic field and spectral age analysis of SDSS J114657.59+403708.6 at z = 5.01 may indicate that the turnover is not caused by synchrotron self-absorption, but rather by free-free absorption by the high-density medium in the nuclear region. Alternatively, the apparent turnover may be an artifact of source variability. Finally, we calculated the radio loudness R2500 Å for our sample, which spans a very wide range from 12−13+13 to 4982−254+279.

scholarly journals Counts and Colors of Faint Galaxies

1980 ◽  
Vol 92 ◽  
pp. 9-15
Author(s):  
Richard G. Kron
Keyword(s):  
Galaxy Evolution ◽  
Rest Frame ◽  
Spectral Energy ◽  
Measured Quantity ◽  
Energy Distributions ◽  
Color Distribution ◽  
Number Magnitude ◽  
Redshift Galaxy ◽  
Wide Range ◽  
Apparent Color

The color distribution of faint galaxies is an observational dimension which has not yet been fully exploited, despite the important constraints obtainable for galaxy evolution and cosmology. Number-magnitude counts alone contain very diluted information about the state of things because galaxies from a wide range in redshift contribute to the counts at each magnitude. The most-frequently-seen type of galaxy depends on the luminosity function and the relative proportions of galaxies of different spectral classes. The addition of color as a measured quantity can thus considerably sharpen the interpretation of galaxy counts since the apparent color depends on the redshift and rest-frame spectrum. To a first approximation two colors for a galaxy can determine a redshift and a spectral class, because redshift loci in a color-color diagram run roughly parallel to each other, and roughly perpendicular to the zero-redshift galaxy “main sequence” (Tinsley 1977a, Pence 1976) for small redshift. This game becomes more and more uncertain at higher redshift, because the systematics of galaxy UV spectral energy distributions are not well known, and what is known is not well understood (Code and Welch 1979). Redshifts for some random sample of faint galaxies is required to pin down the color-redshift relations; steps in this direction have already been taken by E. Turner. The reason for stressing colors, as opposed to redshifts, is that colors can be obtained relatively easily for large samples of faint galaxies if panoramic detectors are used: indeed, colors are not much more difficult to obtain than magnitudes.

scholarly journals Isolating the jet in broadband spectra of XBs

2010 ◽  
Vol 6 (S275) ◽  
pp. 317-318
Author(s):  
David M. Russell ◽  
Fraser Lewis ◽  
Dipankar Maitra ◽  
Robert J. H. Dunn ◽  
Sera Markoff ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Power Law ◽  
Spectral Energy ◽  
Synchrotron Emission ◽  
Energy Distributions ◽  
X Ray ◽  
Relativistic Jet ◽  
Hard State ◽  
X Ray Binaries

AbstractMost accretion-powered relativistic jet sources in our Galaxy are transient X-ray binaries (XBs). Efforts to coordinate multiwavelength observations of these objects have improved dramatically over the last decade. Now the challenge is to interpret broadband spectral energy distributions (SEDs) of XBs that are well sampled in both wavelength and time. Here we focus on the evolution of the jet in their broadband spectra. Some of the most densely sampled broadband SEDs of a neutron star transient (IGR J00291+5934) are used to constrain the optically thick–thin break in the jet spectrum. For the black hole transient XTE J1550-564, infrared – X-ray correlations, evolution of broadband spectra and timing signatures indicate that synchrotron emission from the jet likely dominates the X-ray power law at low luminosities (~(2 × 10−4 − 2 × 10−3) LEdd) during the hard state outburst decline.

scholarly journals Average radio spectral energy distribution of highly star-forming galaxies

2017 ◽  
Vol 12 (S333) ◽  
pp. 191-194
Author(s):  
K. Tisanić ◽  
V. Smolčić ◽  
J. Delhaize ◽  
M. Novak ◽  
H. Intema ◽  
...  
Keyword(s):  
Power Law ◽  
Rest Frame ◽  
Spectral Energy Distribution ◽  
Spectral Energy ◽  
Frequency Range ◽  
Complete Sample ◽  
Energy Distributions ◽  
Star Forming ◽  
Root Cause ◽  
Frame Frequency

AbstractThe infrared-radio correlation (IRRC) offers a way to assess star formation from radio emission. Multiple studies found the IRRC to decrease with increasing redshift. This may in part be due to the lack of knowledge about the possible radio spectral energy distributions (SEDs) of star-forming galaxies. We constrain the radio SED of a complete sample of highly star-forming galaxies (SFR > 100 M⊙/ yr) based on the VLA-COSMOS 1.4 GHz Joint and 3 GHz Large Project catalogs. We reduce archival GMRT 325 MHz and 610 MHz observations, broadening the rest-frame frequency range to 0.3-15 GHz. Employing survival analysis and fitting a double power law SED, we find that the slope steepens from a spectral index of α1 = 0.51±0.04 below 4.5 GHz to α2 = 0.98±0.07 above 4.5 GHz. Our results suggest that the use of a K-correction assuming a single power-law radio SED for star forming galaxies is likely not the root cause of the IRRC trend.

scholarly journals The Optical/Near-IR Colours of Red Quasars

2000 ◽  
Vol 17 (1) ◽  
pp. 56-71 ◽  
Author(s):  
Paul J. Francis ◽  
Matthew T. Whiting ◽  
Rachel L. Webster
Keyword(s):  
Power Law ◽  
High Redshift ◽  
Sloan Digital Sky Survey ◽  
Spectral Energy ◽  
Spectral Energy Distributions ◽  
Energy Distributions ◽  
Red Power ◽  
Near Ir ◽  
Sky Survey ◽  
Ir Photometry

AbstractWe present quasi-simultaneous multi-colour optical/near-IR photometry for 157 radio selected quasars, forming an unbiassed sub-sample of the Parkes Flat-Spectrum Sample. Data are also presented for 12 optically selected QSOs, drawn from the Large Bright QSO Survey. The spectral energy distributions of the radio- and optically-selected sources are quite different. The optically selected QSOs are all very similar: they have blue spectral energy distributions curving downwards at shorter wavelengths. Roughly 90% of the radio-selected quasars have roughly power-law spectral energy distributions, with slopes ranging from Fv∝v0 to Fv∝v−2. The remaining 10% have spectral energy distributions showing sharp peaks: these are radio galaxies and highly reddened quasars. Four radio sources were not detected down to magnitude limits of H ∼ 19·6. These are probably high redshift (z > 3) galaxies or quasars. We show that the colours of our red quasars lie close to the stellar locus in the optical: they will be hard to identify in surveys such as the Sloan Digital Sky Survey. If near-IR photometry is added, however, the red power-law sources can be clearly separated from the stellar locus: IR surveys such as 2MASS should be capable of finding these sources on the basis of their excess flux in the K-band.

scholarly journals Identifications of Faint IRAS Sources

1996 ◽  
Vol 171 ◽  
pp. 402-402
Author(s):  
M.W. Kümmel ◽  
S.J. Wagner
Keyword(s):  
Broad Band ◽  
Far Infrared ◽  
Power Laws ◽  
Point Sources ◽  
Spectral Energy ◽  
Energy Distributions ◽  
The North ◽  
Luminosity Functions ◽  
Error Circle ◽  
Radio Band

From overlapping scans in the IRAS all-sky survey and additional pointed observations the deepest far infrared survey before ISO exists in the region around the North Ecliptic Pole (NEP) (Hacking P. and Houck J.R., ApJS 63 p. 311). This survey contains detections up to 10 and fluxes up to 100 times fainter than the IRAS survey. In the central square degree around the NEP we combine the far IR-survey with deep radio data at 151 MHz and 1.5 GHz (Visser, A.E. et al., A&AS 110 p. 419, Kollgaard, R.I. et al., ApJS 93 p. 145) and own observation at 2.2μm (K′) and 435nm (B). The error circle around the IRAS source was chosen to include the true source with 85% probability (1.4 sigma). For 29 of the 32 IRAS sources we found at least one possible counterpart. Ten of the objects have multiple (up to four) counterparts in K′. Four of the IRAS sources have counterparts in the 1.5 GHz survey. The higher accuracy of the radio position (∼ 1″) allowed an unambiguous identification of the K′ counterpart. None of the IRAS sources could be found in the 151 MHz survey. The broad band spectra of the three galaxies with measured radio flux exhibit maximum emission between the radio band and 100μm which corresponds to emission by cool dust (< 50 K). Contrary to the infrared luminosity functions at 12μm and 60μm which show power laws, the K′ luminosity function is bimodal. The brightest K′ objects are all point sources. Due to the small number statistics the power law indices of the luminosity functions can not be distinguished. We find a linear relationship between the K′ flux and the flux at 60μm and 12μm over at least one decade. The large deviations by individual sources make an identification of the correct counterpart through this relation impossible. The spectral energy distributions of unambiguously identified sources span only one decade in energy (vSv), i.e. they have flat energy distributions. This suggests an identification of K′ objects with flat energy distribution in case of multiple counterparts.

scholarly journals ISO Observations of AGN and Ultraluminous IR Galaxies

1998 ◽  
Vol 11 (2) ◽  
pp. 1131-1133 ◽  
Author(s):  
Alan F. M. Moorwood
Keyword(s):  
Ionization Potential ◽  
Elliptical Galaxy ◽  
Emission Lines ◽  
Spectral Energy ◽  
High Excitation ◽  
Low Resolution ◽  
Energy Distributions ◽  
Diagnostic Features ◽  
Wide Range ◽  
First Time

All the ISO instruments are contributing to the study of activity in galaxies of essentially all types. Although AGN's as such are pointlike, the beautiful CAM image of CenA shown by Catherine Cesarsky has given us the clearest view so far of its visually obscured nucleus and surrounding spiral disc embedded in an elliptical galaxy. The CAM CVF is also providing spectral images of the PAH features and important diagnostic ionic lines (e.g [NeII] and [NeIII]) in the circumnuclar regions of AGN and merging starburst systems (Vigroux et al., 1996). PHT is providing detailed spectral energy distributions over the complete 2.5-240µm range and PHTS is proving invaluable for assembling a catalogue of low resolution (R ⋍ 90) galaxy spectra covering the 6-12µm PAH features. SWS and LWS are generating higher resolution (R ⋍ 2000-200) spectra over the range 2.5-200µm such as that shown in Fig. 1. of the Circinus galaxy which exhibits both AGN and starburst activity and well illustrates the wide range of diagnostic features, many seen for the first time, accessible to ISO studies of galaxies. It shows the overall continuum with a peak around 100µm; PAH features and Si absorption which dominate the spectrum around 10µm; H recombination lines; H2 pure rotational emission lines; low ionization potential ionic lines excited by starburst activity and high excitation lines (up to ⋍ 300eV) excited by the visually obscured AGN.

scholarly journals The VLA-COSMOS 3 GHz Large Project: Average radio spectral energy distribution of highly star-forming galaxies

2019 ◽  
Vol 621 ◽  
pp. A139 ◽  
Author(s):  
K. Tisanić ◽  
V. Smolčić ◽  
J. Delhaize ◽  
M. Novak ◽  
H. Intema ◽  
...  
Keyword(s):  
Survival Analysis ◽  
Energy Distribution ◽  
Power Law ◽  
Rest Frame ◽  
Spectral Energy Distribution ◽  
Spectral Energy ◽  
Radio Luminosity ◽  
Star Forming ◽  
The Impact ◽  
Frame Frequency

We construct the average radio spectral energy distribution (SED) of highly star-forming galaxies (HSFGs) up to z ∼ 4. Infrared and radio luminosities are bound by a tight correlation that is defined by the so-called q parameter. This infrared–radio correlation provides the basis for the use of radio luminosity as a star-formation tracer. Recent stacking and survival analysis studies find q to be decreasing with increasing redshift. It was pointed out that a possible cause of the redshift trend could be the computation of rest-frame radio luminosity via a single power-law assumption of the star-forming galaxies’ (SFGs) SED. To test this, we constrained the shape of the radio SED of a sample of HSFGs. To achieve a broad rest-frame frequency range, we combined previously published Very Large Array observations of the COSMOS field at 1.4 GHz and 3 GHz with unpublished Giant Meterwave Radio Telescope (GMRT) observations at 325 MHz and 610 MHz by employing survival analysis to account for non-detections in the GMRT maps. We selected a sample of HSFGs in a broad redshift range (z ∈ [0.3, 4],  SFR ≥ 100 M⊙ yr−1) and constructed the average radio SED. By fitting a broken power-law, we find that the spectral index changes from α1 = 0.42 ± 0.06 below a rest-frame frequency of 4.3 GHz to α2 = 0.94 ± 0.06 above 4.3 GHz. Our results are in line with previous low-redshift studies of HSFGs ( SFR >  10 M⊙  yr−1) that show the SED of HSFGs to differ from the SED found for normal SFGs ( SFR <  10 M⊙ yr−1). The difference is mainly in a steeper spectrum around 10 GHz, which could indicate a smaller fraction of thermal free–free emission. Finally, we also discuss the impact of applying this broken power-law SED in place of a simple power-law in K-corrections of HSFGs and a typical radio SED for normal SFGs drawn from the literature. We find that the shape of the radio SED is unlikely to be the root cause of the q − z trend in SFGs.

scholarly journals THE REST-FRAME UV-TO-OPTICAL COLORS AND SPECTRAL ENERGY DISTRIBUTIONS OFz∼ 4-7 GALAXIES

2012 ◽  
Vol 755 (2) ◽  
pp. 148 ◽  
Author(s):  
Valentino González ◽  
Rychard J. Bouwens ◽  
Ivo Labbé ◽  
Garth Illingworth ◽  
Pascal Oesch ◽  
...  
Keyword(s):  
Rest Frame ◽  
Spectral Energy ◽  
Spectral Energy Distributions ◽  
Energy Distributions

scholarly journals Modeling the Orientation of AGN

2009 ◽  
Vol 5 (S267) ◽  
pp. 107-107
Author(s):  
Emily Down
Keyword(s):  
Accretion Disk ◽  
Power Law ◽  
Emission Lines ◽  
Spectral Energy ◽  
Spectral Energy Distributions ◽  
Energy Distributions ◽  
Near Ir ◽  
Bayesian Evidence ◽  
Hα Emission

The orientation of nineteen 0.8< z < 2.3 radio-loud quasars was measured using two independent methods. First, Hα was observed in the near IR using ISAAC at the VLT. The complex Hα emission lines were fitted with a range of models, some including emission from a flattened, extended accretion disk following Chen & Halpern (1989). The models were compared using the Bayesian evidence, and the disk axis angles recovered. Second, models were fitted to the ~10 MHz to 20 GHz radio spectral energy distributions (SEDs) to recover the jet angles, assuming that the emission is comprised of a broken power law arising from the radio lobes plus a Doppler-boosted core.

scholarly journals Angular clustering of point sources at 150 MHz in the TGSS survey

2019 ◽  
Vol 485 (4) ◽  
pp. 5891-5896 ◽  
Author(s):  
Sandeep Rana ◽  
Jasjeet S Bagla
Keyword(s):  
Correlation Function ◽  
Power Law ◽  
Low Frequency ◽  
Point Sources ◽  
Radio Sources ◽  
Redshift Distribution ◽  
Intensity Mapping ◽  
Flux Limit ◽  
Sky Survey ◽  
Angular Correlation Function

Abstract We study the angular clustering of point sources in The GMRT (Giant Metrewave Radio Telescope) Sky Survey (TGSS). The survey at 150 MHz with δ &gt; −53.5° has a sky coverage of 3.6π steradians, i.e. $90{{\ \rm per\ cent}}$ of the whole sky. We created subsamples by applying different total flux thresholds limit (Sflux ≫ 5σ) for good completeness and measured the angular correlation function ω(θ) of point sources at large scales (≥1°). We find that the amplitude of angular clustering is higher for brighter subsamples; this indicates that higher threshold flux samples are hosted by massive haloes and cluster strongly: this conclusion is based on the assumption that the redshift distribution of sources does not change with flux and this is supported by models of radio sources. We compare our results with other low-frequency studies of clustering of point sources and verify that the amplitude of clustering varies with the flux limit. We quantify this variation as a power-law dependence of the amplitude of correlation function with the flux limit. This dependence can be used to estimate foreground contamination due to clustering of point sources for low-frequency H i intensity mapping surveys for studying the epoch of reionization.

Sign in / Sign up

Export Citation Format

Share Document