Galaxy And Mass Assembly (GAMA): The sSFR-M* relation part I – σsSFR-M* as a function of sample, SFR indicator and environment
L. J. M. DaviesClaudia del P. LagosAntonios KatsianisA. S. G. RobothamL. CorteseSimon P. DriverM. N. BremerM. J. I. BrownSarah BroughM. E. CluverMeiert W. GrootesBenne W. HolwerdaM. S. OwersS. Phillipps
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Abstract:
Recently a number of studies have proposed that the dispersion along the star formation rate - stellar mass relation ($\sigma_{\mathrm{sSFR}}$-M$_{*}$) is indicative of variations in star-formation history (SFH) driven by feedback processes. They found a 'U'-shaped dispersion and attribute the increased scatter at low and high stellar masses to stellar and active galactic nuclei feed-back respectively. However, measuring $\sigma_{\mathrm{sSFR}}$ and the shape of the $\sigma_{\mathrm{sSFR}}$-M$_{*}$ relation is problematic and can vary dramatically depending on the sample selected, chosen separation of passive/star-forming systems, and method of deriving star-formation rates ($i.e.$ H$\alpha$ emission vs spectral energy distribution fitting). As such, any astrophysical conclusions drawn from measurements of $\sigma_{\mathrm{sSFR}}$ must consider these dependencies. Here we use the Galaxy And Mass Assembly survey to explore how $\sigma_{\mathrm{sSFR}}$ varies with SFR indicator for a variety of selections for disc-like `main sequence' star-forming galaxies including colour, star-formation rate, visual morphology, bulge-to-total mass ratio, S\'{e}rsic index and mixture modelling. We find that irrespective of sample selection and/or SFR indicator, the dispersion along the sSFR-M$_{*}$ relation does follow a 'U'-shaped distribution. This suggests that the shape is physical and not an artefact of sample selection or method. We then compare the $\sigma_{\mathrm{sSFR}}$-M$_{*}$ relation to state-of-the-art hydrodynamical and semi-analytic models and find good agreement with our observed results. Finally, we find that for group satellites this 'U'-shaped distribution is not observed due to additional high scatter populations at intermediate stellar masses.Keywords:
Sigma
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Star (game theory)
Velocity dispersion
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The observed relation between supermassive black hole (SMBH) mass (M•) and bulge stellar velocity dispersion (σ*) is described by log M• = α + βlog(σ*/200 km s-1). As this relation has important implications for models of galaxy and SMBH formation and evolution, there continues to be great interest in adding to the M• catalog. The "sphere of influence" (ri) argument uses spatial resolution to exclude some M• estimates and pre-select additional galaxies for further SMBH studies. This Letter quantifies the effects of applying the ri argument to a population of galaxies and SMBHs that do not follow the M•–σ* relation. All galaxies with known values of σ*, closer than 100 Mpc, are given a random M• and selected when ri is spatially resolved. These random SMBHs produce a M•–σ* relation of α = 8.3 ± 0.2, β = 4.0 ± 0.3, consistent with observed values. Consequently, future proposed M• estimates should not be justified solely on the basis of resolving ri. This Letter shows that the observed M•–σ* relation may simply be a result of available spatial resolution. However, it also implies that the observed M•–σ* relation defines an upper limit. This potentially provides valuable new insight into the processes of galaxy and SMBH formation and evolution.
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There is an intimate link between supermassive black hole (SMBH) mass (M) and the stellar velocity dispersion (sigma) of the host bulge. This has a fundamental impact on our understanding of galaxy and SMBH formation and evolution. However, the scatter, slope and zero-point of the relation is a subject of some debate. For any progress to be made on this relation, the established values of M and sigma must be robust. Over 50% of current M estimates have been made using the technique of stellar dynamics. However, there is serious concern over this method that prompts their re-evaluation. In addition, it is not clear how best to define sigma. The aim of the M-Sigma Project is to use STIS long-slit spectroscopy, integral field spectroscopy and the latest stellar models, to best estimate the values of M and sigma in as many cases as possible. The project will determine the most appropriate properties of the M-Sigma relation itself.
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We present a second dataset of absorption spectroscopy on the inner region of spiral galaxies. We have determined the central velocity dispersion for 42 Sa-Sc objects and, for 32 of them, stellar rotation curves and velocity-dispersion profiles. Some of these profiles are limited to the bulge, some others do reach a region dominated by the luminosity of the disk. These data are intended to provide basic material for the study of the mass distribution and dynamical status in the central regions of spiral galaxies. Although no elaborate bulge-and-disk photometric decomposition is performed, we estimate the effects of limited resolution and contamination by disk light on the central velocity dispersion of the bulge. All the material presented in this paper, in particular the spectra, is available on-line.
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Barred spiral galaxy
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Recent photometric studies have shown that early-type galaxies at fixed stellar mass were smaller and denser at earlier times. In this paper we assess that finding by deriving the dynamical mass of such a compact quiescent galaxy at z=1.8. We have obtained a high-quality spectrum with full UV-NIR wavelength coverage of galaxy NMBS-C7447 using X-Shooter on the VLT. We determined a velocity dispersion of 294 +- 51 km/s. Given this velocity dispersion and the effective radius of 1.64 +- 0.15 kpc (as determined from HST-WFC3 F160W observations) we derive a dynamical mass of 1.7 +- 0.5 x 10^11 Msun. Comparison of the full spectrum with stellar population synthesis models indicates that NMBS-C774 has a relatively young stellar population (0.40 Gyr) with little or no star formation and a stellar mass of ~1.5 x 10^11 Msun. The dynamical and photometric stellar mass are in good agreement. Thus, our study supports the conclusion that the mass densities of quiescent galaxies were indeed higher at earlier times, and this earlier result is not caused by systematic measurement errors. By combining available spectroscopic measurements at different redshifts, we find that the velocity dispersion at fixed dynamical mass was a factor of ~1.8 higher at z=1.8 compared to z=0. Finally, we show that the apparent discrepancies between the few available velocity dispersion measurements at z>1.5 are consistent with the intrinsic scatter of the mass-size relation.
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Stellar population
Effective radius
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