Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDynamical Properties of z~2 Star Forming Galaxies and a Universal Star Formation Relation
241
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present the first comparison of the dynamical properties of different samples of z~1.4-3.4 star forming galaxies from spatially resolved imaging spectroscopy from SINFONI/VLT integral field spectroscopy and IRAM CO millimeter interferometry. Our samples include 16 rest-frame UV-selected, 16 rest-frame optically-selected and 13 submillimeter galaxies (SMGs). We find that restframe UV- and optically bright (K<20) z~2 star forming galaxies are dynamically similar, and follow the same velocity-size relation as disk galaxies at z~0. In the theoretical framework of rotating disks forming from dissipative collapse in dark matter halos, the two samples require a spin parameter ranging from 0.06 to 0.2. In contrast bright SMGs have larger velocity widths and are much more compact. Hence, SMGs have lower angular momenta and higher matter densities than either of the UV- or optically selected populations. This indicates that dissipative major mergers may dominate the SMGs population, resulting in early spheroids, and that the majority of UV/optically bright galaxies have evolved less violently [...]. These early disks may later evolve into spheroids via disk instabilities or mergers. Because of their small sizes and large densities, SMGs lie at the high surface density end of a universal (out to z=2.5) Schmidt-Kennicutt relation between gas surface density and star formation rate surface density with a slope of ~1.7.
rate research
Read More
We study the evolution of the core (r<1 kpc) and effective (r<r_e) stellar-mass surface densities, in star-forming and quiescent galaxies. Since z=3, both populations occupy distinct, linear relations in log(Sigma_e) and log(Sigma_1) vs. log(M). These structural relations exhibit slopes and scatter that remain almost constant with time while their normalizations decline. For SFGs, the normalization declines by less than a factor of 2 from z=3, in both Sigma_e and Sigma_1. Such mild declines suggest that SFGs build dense cores by growing along these relations. We define this evolution as the structural main sequence (Sigma-MS). Quiescent galaxies follow different relations (Sigma^Q_e, Sigma^Q_1) off the Sigma-MS by having higher densities than SFGs of the same mass and redshift. The normalization of Sigma^Q_e declines by a factor of 10 since z=3, but only a factor of 2 in Sigma^Q_1. Thus, the common denominator for quiescent galaxies at all redshifts is the presence of a dense stellar core, and the formation of such cores in SFGs is the main requirement for quenching. Expressed in 2D as deviations off the SFR-MS and off Sigma^Q_1 at each redshift, the distribution of massive galaxies forms a universal, L-shaped sequence that relates two fundamental physical processes: compaction and quenching. Compaction is a process of substantial core-growth in SFGs relative to that in the Sigma-MS. This process increases the core-to-total mass and Sersic index, thereby, making compact SFGs. Quenching occurs once compact SFGs reach a maximum central density above Sigma^Q_1 > 9.5 M_sun/kpc^2. This threshold provides the most effective selection criterion to identify the star-forming progenitors of quiescent galaxies at all redshifts.
We study the star formation rates (SFRs) of galaxies as a function of local galaxy density at 0.6<z<0.9. We used a low-dispersion prism in IMACS on the 6.5-m Baade (Magellan I) telescope to obtain spectra and measured redshifts to a precision of sigma_z/(1+z)=1% for galaxies with z<23.3 AB mag. We utilized a stellar mass-limited sample of 977 galaxies above M>1.8x10^{10} Msun to conduct our main analysis. With three different SFR indicators, (1) Spitzer MIPS 24-micron imaging, (2) SED fitting, and (3) [OII]3727 emission, we find the median specific SFR (SSFR) and SFR to decline from the low-density field to the cores of groups and a rich cluster. For the SED and [OII] based SFRs, the decline in SSFR is roughly an order of magnitude while for the MIPS based SFRs, the decline is a factor of ~4. We find approximately the same magnitude of decline in SSFR even after removing the sample of galaxies near the cluster. Galaxies in groups and a cluster at these redshifts therefore have lower star formation (SF) activity than galaxies in the field, as is the case at z~0. We investigated whether the decline in SFR with increasing density is caused by a change in the proportion of quiescent and star forming galaxies (SFGs) or by a decline in the SFRs of SFGs. Using the rest-frame U-V and V-J colors to distinguish quiescent galaxies from SFGs we find the fraction of quiescent galaxies increases from ~32% to 79% from low to high density. In addition, we find the SSFRs of SFGs, selected based on U-V and V-J colors, to decline with increasing density by factors of ~5-6 for the SED and [OII] based SFRs. The MIPS based SSFRs for SFGs decline with a shallower slope. The order of magnitude decline in the SSFR-density relation at 0.6<z<0.9 is therefore driven by both a combination of declining SFRs of SFGs as well as a changing mix of SFGs and quiescent galaxies [ABRIDGED].
We have used the Spitzer Space Telescope to study the dust properties of a sample of star-forming dwarf galaxies. The differences in the mid-infrared spectral energy distributions for these galaxies which, in general, are low metallicity systems, indicate differences in the physical properties, heating, and/or distribution of the dust. Specifically, these galaxies have more hot dust and/or very small grains and less PAH emission than either spiral or higher luminosity starburst galaxies. As has been shown in previous studies, there is a gradual decrease in PAH emission as a function of metallicity. Because much of the energy from star formation in galaxies is re-radiated in the mid-infrared, star-formation rate indicators based on both line and continuum measurements in this wavelength range are coming into more common usage. We show that the variations in the interstellar medium properties of galaxies in our sample, as measured in the mid-infrared, result in over an order of magnitude spread in the computed star-formation rates.
We use new ALMA observations to investigate the connection between dense gas fraction, star formation rate, and local environment across the inner region of four local galaxies showing a wide range of molecular gas depletion times. We map HCN (1-0), HCO$^+$ (1-0), CS (2-1), $^{13}$CO (1-0), and C$^{18}$O (1-0) across the inner few kpc of each target. We combine these data with short spacing information from the IRAM large program EMPIRE, archival CO maps, tracers of stellar structure and recent star formation, and recent HCN surveys by Bigiel et al. and Usero et al. We test the degree to which changes in the dense gas fraction drive changes in the SFR. $I_{HCN}/I_{CO}$ (tracing the dense gas fraction) correlates strongly with $I_{CO}$ (tracing molecular gas surface density), stellar surface density, and dynamical equilibrium pressure, $P_{DE}$. Therefore, $I_{HCN}/I_{CO}$ becomes very low and HCN becomes very faint at large galactocentric radii, where ratios as low as $I_{HCN}/I_{CO} sim 0.01$ become common. The apparent ability of dense gas to form stars, $Sigma_{SFR}/Sigma_{dense}$ (where $Sigma_{dense}$ is traced by the HCN intensity and the star formation rate is traced by a combination of H$alpha$ and 24$mu$m emission), also depends on environment. $Sigma_{SFR}/Sigma_{dense}$ decreases in regions of high gas surface density, high stellar surface density, and high $P_{DE}$. Statistically, these correlations between environment and both $Sigma_{SFR}/Sigma_{dense}$ and $I_{HCN}/I_{CO}$ are stronger than that between apparent dense gas fraction ($I_{HCN}/I_{CO}$) and the apparent molecular gas star formation efficiency $Sigma_{SFR}/Sigma_{mol}$. We show that these results are not specific to HCN.
We derive two-dimensional dust attenuation maps at $sim1~mathrm{kpc}$ resolution from the UV continuum for ten galaxies on the $zsim2$ Star-Forming Main Sequence (SFMS). Comparison with IR data shows that 9 out of 10 galaxies do not require further obscuration in addition to the UV-based correction, though our sample does not include the most heavily obscured, massive galaxies. The individual rest-frame $V$-band dust attenuation (A$_{rm V}$) radial profiles scatter around an average profile that gently decreases from $sim1.8$ mag in the center down to $sim0.6$ mag at $sim3-4$ half-mass radii. We use these maps to correct UV- and H$alpha$-based star-formation rates (SFRs), which agree with each other. At masses $<10^{11}~M_{rm sun}$, the dust-corrected specific SFR (sSFR) profiles are on average radially constant at a mass-doubling timescale of $sim300~mathrm{Myr}$, pointing at a synchronous growth of bulge and disk components. At masses $>10^{11}~M_{rm sun}$, the sSFR profiles are typically centrally-suppressed by a factor of $sim10$ relative to the galaxy outskirts. With total central obscuration disfavored, this indicates that at least a fraction of massive $zsim2$ SFMS galaxies have started their inside-out star-formation quenching that will move them to the quenched sequence. In combination with other observations, galaxies above and below the ridge of the SFMS relation have respectively centrally-enhanced and centrally-suppressed sSFRs relative to their outskirts, supporting a picture where bulges are built due to gas `compaction that leads to a high central SFR as galaxies move towards the upper envelope of SFMS.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
