Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userConstraints on the Accuracy of Photometric Redshifts Derived from BLAST and Herschel/SPIRE Sub-mm Surveys
60
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
More than 150 galaxies have been detected in blank-field millimetre and sub-millimetre surveys. However the redshift distribution of sub-mm galaxies remains uncertain due to the difficulty in identifying their optical-IR counterparts, and subsequently obtaining their spectroscopic emission-line redshifts. In this paper we discuss results from a Monte-Carlo analysis of the accuracy with which one can determine redshifts from photometric measurements at sub-millimetre-FIR wavelengths. The analysis takes into account the dispersion in colours introduced by including galaxies with a distribution of SEDs, and by including photometric and absolute calibration errors associated with real observations. We present examples of the probability distribution of redshifts for individual galaxies detected in the future BLAST and Herschel/SPIRE surveys. We show that the combination of BLAST and 850um observations constrain the photometric redshifts with sufficient accuracy to pursue a program of spectroscopic follow-up with the 100m GBT.
rate research
Read More
We investigate the potential of submm-mm and submm-mm-radio photometric redshifts using a sample of mm-selected sources as seen at 250, 350 and 500 {mu}m by the SPIRE instrument on Herschel. From a sample of 63 previously identified mm-sources with reliable radio identifications in the GOODS-N and Lockman Hole North fields 46 (73 per cent) are found to have detections in at least one SPIRE band. We explore the observed submm/mm colour evolution with redshift, finding that the colours of mm-sources are adequately described by a modified blackbody with constant optical depth {tau} = ({ u}/{ u}0)^{beta} where {beta} = +1.8 and { u}0 = c/100 {mu}m. We find a tight correlation between dust temperature and IR luminosity. Using a single model of the dust temperature and IR luminosity relation we derive photometric redshift estimates for the 46 SPIRE detected mm-sources. Testing against the 22 sources with known spectroscopic, or good quality optical/near-IR photometric, redshifts we find submm/mm photometric redshifts offer a redshift accuracy of |z|/(1+z) = 0.16 (< |z| >= 0.51). Including constraints from the radio-far IR correlation the accuracy is improved to |z|/(1 + z) = 0.15 (< |z| >= 0.45). We estimate the redshift distribution of mm-selected sources finding a significant excess at z > 3 when compared to ~ 850 {mu}m selected samples.
We measure the local galaxy far-infrared (FIR) 60-to-100 um colour-luminosity distribution using an all-sky IRAS survey. This distribution is an important reference for the next generation of FIR--submillimetre surveys that have and will conduct deep extra-galactic surveys at 250--500 um. With the peak in dust-obscured star-forming activity leading to present-day giant ellipticals now believed to occur in sub-mm galaxies near z~2.5, these new FIR--submillimetre surveys will directly sample the SEDs of these distant objects at rest-frame FIR wavelengths similar to those at which local galaxies were observed by IRAS. We have taken care to correct for temperature bias and evolution effects in our IRAS 60 um-selected sample. We verify that our colour-luminosity distribution is consistent with measurements of the local FIR luminosity function, before applying it to the higher-redshift Universe. We compare our colour-luminosity correlation with recent dust-temperature measurements of sub-mm galaxies and find evidence for pure luminosity evolution of the form (1+z)^3. This distribution will be useful for the development of evolutionary models for BLAST and SPIRE surveys as it provides a statistical distribution of rest-frame dust temperatures for galaxies as a function of luminosity.
We present a comparison between the published optical, IR and CO spectroscopic redshifts of 86 (sub-)mm galaxies and their photometric redshifts as derived from long-wavelength radio-mm-FIR photometric data. The redshift accuracy measured for 13 sub-mm galaxies with at least one robustly determined colour in the radio-mm-FIR regime and additional constraining upper limits is z ~0.3. This accuracy degrades to z~0.65 when only the 1.4GHz/850um spectral index is used, as derived from the analysis of a subsample of 58 galaxies with robustly determined redshifts. Despite the wide range of spectral energy distributions in the local galaxies that are used in an un-biased manner as templates, this analysis demonstrates that photometric redshifts can be effciently derived for sub-mm galaxies with a precision of Delta z < 0.5 using only the rest-frame FIR to radio wavelength data, suficient to guide the tuning of broad-band heterodyne observations (e.g. 100m GBT, 50m LMT, ALMA) or aid their determination in the case of a single line detection by these experiments.
Upon its completion the Herschel ATLAS (H-ATLAS) will be the largest submillimetre survey to date, detecting close to half-a-million sources. It will only be possible to measure spectroscopic redshifts for a small fraction of these sources. However, if the rest-frame spectral energy distribution (SED) of a typical H-ATLAS source is known, this SED and the observed Herschel fluxes can be used to estimate the redshifts of the H-ATLAS sources without spectroscopic redshifts. In this paper, we use a subset of 40 H-ATLAS sources with previously measured redshifts in the range 0.5<z<4.2 to derive a suitable average template for high redshift H-ATLAS sources. We find that a template with two dust components T_c = 23.9 K, T_h = 46.9 K and ratio of mass of cold dust to mass of warm dust of 30.1) provides a good fit to the rest-frame fluxes of the sources in our calibration sample. We use a jackknife technique to estimate the accuracy of the redshifts estimated with this template, finding a root mean square of Delta z/(1+z) = 0.26. For sources for which there is prior information that they lie at z > 1 we estimate that the rms of Delta z/(1+z) = 0.12. We have used this template to estimate the redshift distribution for the sources detected in the H-ATLAS equatorial fields, finding a bimodal distribution with a mean redshift of 1.2, 1.9 and 2.5 for 250, 350 and 500 um selected sources respectively. end{abstract}
We present the sub-millimeter spectra from 450 GHz to 1550 GHz of eleven nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer (SPIRE/FTS) onboard Herschel. We detect CO transitions from J_up = 4 to 12, as well as the two [CI] fine structure lines at 492 and 809 GHz and the [NII] 461 GHz line. We used radiative transfer models to analyze the observed CO spectral line energy distributions (SLEDs). The FTS CO data were complemented with ground-based observations of the low-J CO lines. We found that the warm molecular gas traced by the mid-J CO transitions has similar physical conditions (n_H2 ~ 10^3.2 - 10^3.9 cm^-3 and T_kin ~ 300 - 800 K) in most of our galaxies. Furthermore, we found that this warm gas is likely producing the mid-IR rotational H2 emission. We could not determine the specific heating mechanism of the warm gas, however it is possibly related to the star-formation activity in these galaxies. Our modeling of the [CI] emission suggests that it is produced in cold (T_kin < 30 K) and dense (n_H2 > 10^3 cm^-3) molecular gas. Transitions of other molecules are often detected in our SPIRE/FTS spectra. The HF J=1-0 transition at 1232 GHz is detected in absorption in UGC05101 and in emission in NGC7130. In the latter, near-infrared pumping, chemical pumping, or collisional excitation with electrons are plausible excitation mechanisms likely related to the AGN of this galaxy. In some galaxies few H2O emission lines are present. Additionally, three OH+ lines at 909, 971, and 1033 GHz are identified in NGC7130.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
