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Register a new userTesting Star Formation Laws on Spatially Resolved Regions in a $z approx 4.3$ Starburst Galaxy
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We probe the star formation properties of the gas in AzTEC-1 in the COSMOS field, one of the best resolved and brightest starburst galaxies at $z approx 4.3$, forming stars at a rate > 1000 $mathrm{M_{odot}},mathrm{yr^{-1}}$. Using recent ALMA observations, we study star formation in the galaxy nucleus and an off-center star-forming clump and measure a median star formation rate (SFR) surface density of $Sigma^{mathrm{nucleus}}_{mathrm{SFR}} = 270pm54$ and $Sigma^{mathrm{sfclump}}_{mathrm{SFR}} = 170pm38,mathrm{M_{odot}},mathrm{yr}^{-1},mathrm{kpc}^{-2}$, respectively. Following the analysis by Sharda et al. (2018), we estimate the molecular gas mass, freefall time and turbulent Mach number in these regions to predict $Sigma_{mathrm{SFR}}$ from three star formation relations in the literature. The Kennicutt-Schmidt (Kennicutt 1998, KS) relation, which is based on the gas surface density, underestimates the $Sigma_{mathrm{SFR}}$ in these regions by a factor 2-3. The $Sigma_{mathrm{SFR}}$ we calculate from the single-freefall model of Krumholz et al. 2012 (KDM) is consistent with the measured $Sigma_{mathrm{SFR}}$ in the nucleus and the star-forming clump within the uncertainties. The turbulence-regulated star formation relation by Salim et al. 2015 (SFK) agrees slightly better with the observations than the KDM relation. Our analysis reveals that an interplay between turbulence and gravity can help sustain high SFRs in high-redshift starbursts. It can also be extended to other high- and low-redshift galaxies thanks to the high angular resolution and sensitivity of ALMA observations.
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Using high-resolution (sub-kiloparsec scale) submillimeter data obtained by ALMA, we analyze the star formation rate (SFR), gas content and kinematics in SDP 81, a gravitationally-lensed star-forming galaxy at redshift 3. We estimate the SFR surface density ($Sigma_{mathrm{SFR}}$) in the brightest clump of this galaxy to be $357^{+135}_{-85},mathrm{M_{odot},yr^{-1},kpc^{-2}}$, over an area of $0.07pm0.02,mathrm{kpc}^2$. Using the intensity-weighted velocity of CO$,$(5-4), we measure the turbulent velocity dispersion in the plane-of-the-sky and find $sigma_{mathrm{v,turb}} = 37pm5,mathrm{km,s}^{-1}$ for the star-forming clump, in good agreement with previous estimates along the line of sight. Our measurements of gas surface density, freefall time and turbulent Mach number reveal that the role of turbulence is vital to explaining the observed SFR in this clump. While the Kennicutt Schmidt (KS) relation predicts a SFR surface density of $Sigma_{mathrm{SFR,KS}} = 52pm17,mathrm{M_{odot},yr^{-1},kpc^{-2}}$, the single-freefall model by Krumholz, Dekel and McKee (KDM) predicts $Sigma_{mathrm{SFR,KDM}} = 106pm37,mathrm{M_{odot},yr^{-1},kpc^{-2}}$. In contrast, the multi-freefall (turbulence) model by Salim, Federrath and Kewley (SFK) gives $Sigma_{mathrm{SFR,SFK}} = 491^{+139}_{-194},mathrm{M_{odot},yr^{-1},kpc^{-2}}$. Although the SFK relation overestimates the SFR in this clump (possibly due to the ignorance of magnetic field), it provides the best prediction among the available models. Finally, we compare the star formation and gas properties of this high-redshift galaxy to local star-forming regions and find that the SFK relation provides the best estimates of SFR in both local and high-redshift galaxies.
SPT0346-52 is one of the most most luminous and intensely star-forming galaxies in the universe, with L_FIR > 10^13 L_sol and Sigma_SFR ~ 4200 M_sol yr^-1 kpc^-2. In this paper, we present ~0.15 ALMA observations of the [CII]158micron emission line in this z=5.7 dusty star-forming galaxy. We use a pixellated lensing reconstruction code to spatially and kinematically resolve the source-plane [CII] and rest-frame 158 micron dust continuum structure at ~700 pc (~0.12) resolution. We discuss the [CII] deficit with a pixellated study of the L_[CII]/L_FIR ratio in the source plane. We find that individual pixels within the galaxy follow the same trend found using unresolved observations of other galaxies, indicating that the deficit arises on scales <700 pc. The lensing reconstruction reveals two spatially and kinematically separated components (~1 kpc and ~500 km s^-1 apart) connected by a bridge of gas. Both components are found to be globally unstable, with Toomre Q instability parameters << 1 everywhere. We argue that SPT0346-52 is undergoing a major merger, which is likely driving the intense and compact star formation.
We present Lightning, a new spectral energy distribution (SED) fitting procedure, capable of quickly and reliably recovering star formation history (SFH) and extinction parameters. The SFH is modeled as discrete steps in time. In this work, we assumed lookback times of 0-10 Myr, 10-100 Myr, 0.1-1 Gyr, 1-5 Gyr, and 5-13.6 Gyr. Lightning consists of a fully vectorized inversion algorithm to determine SFH step intensities and combines this with a grid-based approach to determine three extinction parameters. We apply our procedure to the extensive FUV-to-FIR photometric data of M51, convolved to a common spatial resolution and pixel scale, and make the resulting maps publicly available. We recover, for M51a, a peak star formation rate (SFR) between 0.1 and 5 Gyr ago, with much lower star formation activity over the last 100 Myr. For M51b, we find a declining SFR toward the present day. In the outskirt regions of M51a, which includes regions between M51a and M51b, we recover a SFR peak between 0.1 and 1 Gyr ago, which corresponds to the effects of the interaction between M51a and M51b. We utilize our results to (1) illustrate how UV+IR hybrid SFR laws vary across M51, and (2) provide first-order estimates for how the IR luminosity per unit stellar mass varies as a function of the stellar age. From the latter result, we find that IR emission from dust heated by stars is not always associated with young stars, and that the IR emission from M51b is primarily powered by stars older than 5 Gyr.
Bars inhabit the majority of local-Universe disk galaxies and may be important drivers of galaxy evolution through the redistribution of gas and angular momentum within disks. We investigate the star formation and gas properties of bars in galaxies spanning a wide range of masses, environments, and star formation rates using the MaNGA galaxy survey. Using a robustly-defined sample of 684 barred galaxies, we find that fractional (or scaled) bar length correlates with the hosts offset from the star-formation main sequence. Considering the morphology of the H$alpha$ emission we separate barred galaxies into different categories, including barred, ringed, and central configurations, together with H$alpha$ detected at the ends of a bar. We find that only low-mass galaxies host star formation along their bars, and that this is located predominantly at the leading edge of the bar itself. Our results are supported by recent simulations of massive galaxies, which show that the position of star formation within a bar is regulated by a combination of shear forces, turbulence and gas flows. We conclude that the physical properties of a bar are mostly governed by the existing stellar mass of the host galaxy, but that they also play an important role in the galaxys ongoing star formation.
We study the internal gradients of stellar population properties within $1.5;R_{rm e}$ for a representative sample of 721 galaxies with stellar masses ranging between $10^{9};M_{odot}$ to $10^{11.5};M_{odot}$ from the SDSS-IV MaNGA IFU survey. Through the use of our full spectral fitting code FIREFLY, we derive light and mass-weighted stellar population properties and their radial gradients, as well as full star formation and metal enrichment histories. We also quanfify the impact that different stellar population models and full spectral fitting routines have on the derived stellar population properties, and the radial gradient measurements. In our analysis, we find that age gradients tend to be shallow for both early-type and late-type galaxies. {em Mass-weighted} age gradients of early-types are positive ($sim 0.09; {rm dex}/R_{rm e}$) pointing to outside-in progression of star formation, while late-type galaxies have negative {em light-weighted} age gradients ($sim -0.11; {rm dex}/R_{rm e}$), suggesting an inside-out formation of discs. We detect negative metallicity gradients in both early and late-type galaxies, but these are significantly steeper in late-types, suggesting that radial dependence of chemical enrichment processes and the effect of gas inflow and metal transport are far more pronounced in discs. Metallicity gradients of both morphological classes correlate with galaxy mass, with negative metallicity gradients becoming steeper with increasing galaxy mass. The correlation with mass is stronger for late-type galaxies, with a slope of $d( abla [Z/H])/d(log M)sim -0.2pm 0.05;$, compared to $d( abla [Z/H])/d(log M)sim -0.05pm 0.05;$ for early-types. This result suggests that the merger history plays a relatively small role in shaping metallicity gradients of galaxies.
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