Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe formation and assembly of a typical star-forming galaxy at z~3
458
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Recent studies of galaxies ~2-3 Gyr after the Big Bang have revealed large, turbulent rotating systems. The existence of well-ordered rotation in galaxies during this peak epoch of cosmic star formation may suggest that gas accretion through cold streams is likely to be the dominant mode by which most star-forming galaxies at high redshift since major mergers can completely disrupt the observed velocity fields. However poor spatial resolution and sensitivity have hampered this interpretation, limiting the study to the largest and most luminous galaxies, which may have fundamentally different modes of assembly than more typical star forming galaxies. Here we report observations of a typical star forming galaxy at z=3.07 with a linear resolution of ~100 parsec. This spatial sampling is made possible by the combination of gravitational lensing and laser guide star adaptive optics. We find a well-ordered compact source in which molecular gas is being converted efficiently into stars, likely assembling a spheroidal bulge and disk similar to those seen in spiral galaxies at the present day.
rate research
Read More
In these proceedings, we summarize recent results from our SINS VLT/SINFONI integral-field survey, focusing on the 52 detected UV/optically-selected star-forming galaxies at z~2. Our H-alpha emission-line imaging and kinematic data of these systems illustrates that a substantial fraction (> 1/3) of these galaxies are large, rotating disks and that these disks are clumpy, thick, and forming stars rapidly. We compare these systems to local disk scaling relations and find that the backbones of these relations are already in place at z~2. Detailed analysis of the large disks in our sample provides strong evidence that this population cannot result from a merger-dominated formation history and instead must be assembled by the smooth but rapid inflow of gas along filaments. These systems will then secularly evolve from clump-dominated disks to bulge-dominated disks on short timescales, a phenomenon that is observed in our SINS observations and is consistent with predictions from numerical simulations. These results provide new and exciting insights into the formation of bulge-dominated galaxies in the local Universe.
Analyses of high-redshift ultraluminous infrared (IR) galaxies traditionally use the observed optical to submillimeter spectral energy distribution (SED) and estimates of the dynamical mass as observational constraints to derive the star formation rate (SFR), the stellar mass, and age of these objects. An important observational constraint neglected in the analysis is the mass of dust giving rise to the IR emission. In this paper we add this constraint to the analysis of AzTEC-3. Adopting an upper limit to the mass of stars and a bolometric luminosity for this object, we construct stellar and chemical evolutionary scenarios, constrained to produce the inferred dust mass and observed luminosity before the associated stellar mass exceeds the observational limit. We find that the model with a Top Heavy IMF provided the most plausible scenario consistent with the observational constraints. In this scenario the dust formed over a period of ~200 Myr, with a SFR of ~500 Msun/yr. These values for the age and SFR in AzTEC-3 are significantly higher and lower, respectively, from those derived without the dust mass constraint. However, this scenario is not unique, and others cannot be completely ruled out because of the prevailing uncertainties in the age of the galaxy, its bolometric luminosity, and its stellar and dust masses. A robust result of our models is that all scenarios require most of the radiating dust mass to have been accreted in molecular clouds. Our new procedure highlights the importance of a multiwavelength approach, and of the use of dust evolution models in constraining the age and the star formation activity and history in galaxies.
In this letter we report the discovery of a z=4.88 radio galaxy discovered with a new technique which does not rely on pre-selection of a sample based on radio properties such as steep-spectral index or small angular size. This radio galaxy was discovered in the Elais-N2 field and has a spectral index of alpha = 0.75, i.e. not ultra-steep spectrum. It also has a luminosity consistent with being drawn from the break of the radio luminosity function and can therefore be considered as a typical radio galaxy. Using the Spitzer-SWIRE data over this field we find that the host galaxy is consistent with being similarly massive to the lower redshift powerful radio galaxies (~1-3L*). We note however, that at z=4.88 the H-alpha line is redshifted into the IRAC 3.6micron filter and some of the flux in this band may be due to this rather than stellar continuum emission. The discovery of such a distant radio source from our initial spectroscopic observations demonstrate the promise of our survey for finding the most distant radio sources.
Using the VLA and ALMA, we have obtained CO(2-1), [C II], [N II] line emission and multiple dust continuum measurements in a sample of normal galaxies at $z=5-6$. We report the highest redshift detection of low-$J$ CO emission from a Lyman Break Galaxy, at $zsim5.7$. The CO line luminosity implies a massive molecular gas reservoir of $(1.3pm0.3)(alpha_{rm CO}/4.5,M_odot$ (K km s$^{-1}$ pc$^2)^{-1})times10^{11},M_odot$, suggesting low star formation efficiency, with a gas depletion timescale of order $sim$1 Gyr. This efficiency is much lower than traditionally observed in $zgtrsim5$ starbursts, indicating that star forming conditions in Main Sequence galaxies at $zsim6$ may be comparable to those of normal galaxies probed up to $zsim3$ to-date, but with rising gas fractions across the entire redshift range. We also obtain a deep CO upper limit for a Main Sequence galaxy at $zsim5.3$ with $sim3$ times lower SFR, perhaps implying a high $alpha_{rm CO}$ conversion factor, as typically found in low metallicity galaxies. For a sample including both CO targets, we also find faint [N II] 205$,mu$m emission relative to [C II] in all but the most IR-luminous normal galaxies at $z=5-6$, implying more intense or harder radiation fields in the ionized gas relative to lower redshift. These radiation properties suggest that low metallicity may be common in typical $sim$10$^{10},M_odot$ galaxies at $z=5-6$. While a fraction of Main Sequence star formation in the first billion years may take place in conditions not dissimilar to lower redshift, lower metallicity may affect the remainder of the population.
One key problem in astrophysics is understanding how and why galaxies switch off their star formation, building the quiescent population that we observe in the local Universe. From the GAMA and VIPERS surveys, we use spectroscopic indices to select quiescent and candidate transition galaxies. We identify potentially rapidly transitioning post-starburst galaxies, and slower transitioning green-valley galaxies. Over the last 8 Gyrs the quiescent population has grown more slowly in number density at high masses (M$_*>10^{11}$M$_odot$) than at intermediate masses (M$_*>10^{10.6}$M$_odot$). There is evolution in both the post-starburst and green valley stellar mass functions, consistent with higher mass galaxies quenching at earlier cosmic times. At intermediate masses (M$_*>10^{10.6}$M$_odot$) we find a green valley transition timescale of 2.6 Gyr. Alternatively, at $zsim0.7$ the entire growth rate could be explained by fast-quenching post-starburst galaxies, with a visibility timescale of 0.5 Gyr. At lower redshift, the number density of post-starbursts is so low that an unphysically short visibility window would be required for them to contribute significantly to the quiescent population growth. The importance of the fast-quenching route may rapidly diminish at $z<1$. However, at high masses (M$_*>10^{11}$M$_odot$), there is tension between the large number of candidate transition galaxies compared to the slow growth of the quiescent population. This could be resolved if not all high mass post-starburst and green-valley galaxies are transitioning from star-forming to quiescent, for example if they rejuvenate out of the quiescent population following the accretion of gas and triggering of star formation, or if they fail to completely quench their star formation.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
