Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Properties of Sub-mm Galaxies in Hierarchical Models
216
0
0.0
(
0
)
Authors
Mark Swinbank
Ask ChatGPT about the research
No Arabic abstract
We use the combined GALFORM semi-analytical model of galaxy formation and GRASIL spectrophotometric code to investigate the properties of galaxies selected via their sub-mm emission. Our fiducial model has previously been shown to fit the properties of local ULIRGs, as well as the number counts of faint sub-mm galaxies. Here, we test the model in detail by comparing the SEDs and stellar, dynamical, gas and halo masses of sub-mm galaxies against observational data. We precisely mimic the sub-mm and radio selection function of the observations and show that the predicted far-infrared properties of model galaxies with S_850>5mJy and S_1.4>30uJy are in good agreement with observations. Although the dust emission model does not assume a single dust temperature, the far-infrared SEDs are well described by single component modified black-body spectrum with characteristic temperature 32+/-5K. We also find evidence that the observations may have uncovered evolution in the far-infrared--radio relation in ULIRGs out to z~2. We show that the predicted redshift distribution of sub-mm galaxies provides a reasonable fit to the observational data with a median redshift z=2.0, with the radio-selected subset predicted to make up approximately 75% of the population. However, the predicted K-band and mid-infrared (3--8um) flux densities of the sub-mm galaxies (and LBGs) are up to a factor 10x fainter than observed. This discrepancy may indicate that the stellar masses of the sub-mm galaxies in the model are too low: M~10^10Mo, while observations suggest more massive systems, M~10^11Mo. Finally, we discuss the potential modifications to the models which may improve the fit to the observational data. [Abridged]
rate research
Read More
We present a hierarchical galaxy formation model which can account for the number counts of sources detected through their emission at sub-millimetre wavelengths. The first stage in our approach is an ab initio calculation of the star formation histories for a representative sample of galaxies, which is carried out using the semi-analytical galaxy formation model GALFORM. These star formation histories are then input into the spectro-photometric code GRASIL, to produce a spectral energy distribution for each galaxy. Dust extinction and emission are treated self consistently in our model, without having to resort to ad-hoc assumptions about the amount of attenuation by dust or the temperature at which the dust radiates. We argue that it is necessary to modify the form of the stellar initial mass function in starbursts in order to match the observed number of sub-mm sources, if we are to retain the previous good matches enjoyed between observations and model predictions in the local universe. We also list some other observational tests that have been passed by our model.
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.
We studied the global characteristics of dust emission in a large sample of emission-line star-forming galaxies. The sample consists of two subsamples. One subsample (SDSS sample) includes ~4000 compact star-forming galaxies from the SDSS, which were also detected in all four bands at 3.4, 4.6, 12, and 22 mum of the WISE all-sky survey. The second subsample (Herschel sample) is a sample of 28 compact star-forming galaxies observed with Herschel in the FIR range. Data of the Herschel sample were supplemented by the photometric data from the Spitzer observations, GALEX, SDSS, WISE, 2MASS, NVSS, and FIRST surveys, as well as optical and Spitzer spectra and data in sub-mm and radio ranges. It is found that warm dust luminosities of galaxies from the SDSS sample and cold and warm dust luminosities of galaxies from the Herschel sample are strongly correlated with Hbeta luminosities, which implies that one of the main sources of dust heating in star-forming galaxies is ionising UV radiation of young stars. Using the relation between warm and cold dust masses for estimating the total dust mass in star-forming galaxies with an accuracy better than ~0.5 dex is proposed. On the other hand, it is shown for both samples that dust temperatures do not depend on the metallicities. The dust-to-neutral gas mass ratio strongly declines with decreasing metallicity, similar to that found in other studies of local emission-line galaxies, high-redshift GRB hosts, and DLAs. On the other hand, the dust-to-ionised gas mass ratio is about one hundred times as high implying that most of dust is located in the neutral gas. It is found that thermal free-free emission of ionised gas in compact star-forming galaxies might be responsible for the sub-mm emission excess. This effect is stronger in galaxies with lower metallicities and is also positively affected by an increased star-formation rate.
We present near-infrared integral-field spectroscopic observations targeting H$alpha$ in eight sub-millimeter galaxies (SMGs) at $z$=1.3-2.5 using VLT/SINFONI, obtaining significant detections for six of them. The star formation rates derived from the H$alpha$ emission are $sim$100 M$_odot$yr$^{-1}$, which account for only $sim$ 20-30% of the infrared-derived values, thus suggesting that these systems are very dusty. Two of these systems present [NII]/H$alpha$ ratios indicative of the presence of an Active Galactic Nucleus (AGN). We mapped the spatial distribution and kinematics of the star forming regions in these galaxies on kpc-scales. In general, the H$alpha$ morphologies tend to be highly irregular and/or clumpy, showing spatial extents of $sim$3-11~kpc. We find evidence for significant spatial offsets, of $sim$0.1-0.4$$ or 1.2-3.4 kpc, between the H$alpha$ and the continuum emission in three of the sources. Performing a kinemetry analysis we conclude that the majority of the sample is not consistent with disk-like rotation-dominated kinematics. Instead, they tend to show irregular and/or clumpy and turbulent velocity and velocity dispersion fields. This can be interpreted as evidence for scenario in which these extreme star formation episodes are triggered by galaxy-galaxy interactions and major mergers. In contrast to recent results for SMGs, these sources appear to follow the same relations between gas and star forming rate densities as less luminous and/or normal star forming galaxies.
We present the results of our observations of the early stages of the 2012--2013 outburst of the transient black hole X-ray binary (BHXRB), Swift J1745$-$26, with the VLA, SMA, and JCMT (SCUBA--2). Our data mark the first multiple-band mm & sub-mm observations of a BHXRB. During our observations the system was in the hard accretion state producing a steady, compact jet. The unique combination of radio and mm/sub-mm data allows us to directly measure the spectral indices in and between the radio and mm/sub-mm regimes, including the first mm/sub-mm spectral index measured for a BHXRB. Spectral fitting revealed that both the mm (230 GHz) and sub-mm (350 GHz) measurements are consistent with extrapolations of an inverted power-law from contemporaneous radio data (1--30 GHz). This indicates that, as standard jet models predict, a power-law extending up to mm/sub-mm frequencies can adequately describe the spectrum, and suggests that the mechanism driving spectral inversion could be responsible for the high mm/sub-mm fluxes (compared to radio fluxes) observed in outbursting BHXRBs. While this power-law is also consistent with contemporaneous optical data, the optical data could arise from either jet emission with a jet spectral break frequency of $ u_{{rm break}}gtrsim1times10^{14},{rm Hz}$ or the combination of jet emission with a lower jet spectral break frequency of $ u_{{rm break}}gtrsim2times10^{11},{rm Hz}$ and accretion disc emission. Our analysis solidifies the importance of the mm/sub-mm regime in bridging the crucial gap between radio and IR frequencies in the jet spectrum, and justifies the need to explore this regime further.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
