High Star Formation Rate Surface Research Articles

JWST NIRCam + NIRSpec: interstellar medium and stellar populations of young galaxies with rising star formation and evolving gas reservoirs

ABSTRACT We present an interstellar medium and stellar population analysis of three spectroscopically confirmed z > 7 galaxies in the Early Release Observations JWST/NIRCam and JWST/NIRSpec data of the SMACS J0723.3−7327 cluster. We use the Bayesian spectral energy distribution-fitting code prospector with a flexible star formation history (SFH), a variable dust attenuation law, and a self-consistent model of nebular emission (continuum and emission lines). Importantly, we self-consistently fit both the emission line fluxes from JWST/NIRSpec and the broad-band photometry from JWST/NIRCam, taking into account slit-loss effects. We find that these three z=7.6–8.5 galaxies (M⋆ ≈ 108 M⊙) are young with rising SFHs and mass-weighted ages of 3–4 Myr, though we find indications for underlying older stellar populations. The inferred gas-phase metallicities broadly agree with the direct metallicity estimates from the auroral lines. The galaxy with the lowest gas-phase metallicity (Zgas= 0.06 Z⊙) has a steeply rising SFH, is very compact (<0.2 kpc), and has a high star formation rate surface density (ΣSFR ≈ 22 M⊙ yr−1 kpc−2), consistent with rapid gas accretion. The two other objects with higher gas-phase metallicities show more complex multicomponent morphologies on kpc scales, indicating that their recent increase in star formation rate is driven by mergers or internal, gravitational instabilities. We discuss effects of assuming different SFH priors or only fitting the photometric data. Our analysis highlights the strength and importance of combining JWST imaging and spectroscopy for fully assessing the nature of galaxies at the earliest epochs.

A magnified compact galaxy at redshift 9.51 with strong nebular emission lines.

Ultraviolet light from early galaxies is thought to have ionized gas in the intergalactic medium. However, there are few observational constraints on this epoch because of the faintness of those galaxies and the redshift of their optical light into the infrared. We report the observation, in JWST imaging, of a distant galaxy that is magnified by gravitational lensing. JWST spectroscopy of the galaxy, at rest-frame optical wavelengths, detects strong nebular emission lines that are attributable to oxygen and hydrogen. The measured redshift is z = 9.51 ± 0.01, corresponding to 510 million years after the Big Bang. The galaxy has a radius of [Formula: see text] parsecs, which is substantially more compact than galaxies with equivalent luminosity at z ~ 6 to 8, leading to a high star formation rate surface density.

Physical Characterization of Early Galaxies in the Webb’s First Deep Field SMACS J0723.3-7327

This paper highlights initial photometric analyses of JWST NIRCam imaging data in the sightline of SMACS0723, aiming to identify galaxies at redshift z > 7. By applying a conservative Lyman-break selection followed by photometric-redshift analysis and visual inspection, we identify four F090W-dropout and two F150W-dropout sources, three of which were recently confirmed in an independent spectroscopic analysis to z = 7.663, 7.665, and 8.499. We then supplement our sample with a photometric-redshift selection, and identify five additional candidates at 7 < z phot < 13. The NIRCam images clearly resolve all sources and reveal their subgalactic components that were not resolved/detected in the previous imaging by Hubble Space Telescope. Our spectral energy distribution analysis reveals that the selected galaxies are characterized by young stellar populations (median age of ∼50 Myr) of subsolar metallicity (∼0.2 Z ⊙) and little dust attenuation (A V ∼ 0.5). In several cases, we observe extreme Hβ+[O iii] lines being captured in the F444W band and seen as color excess, which is consistent with their observed high star formation rate surface density. Eight of the 11 sources identified in this study appear in at least one of the recent studies (Adams et al.; Atek et al.; Donnan et al.; Harikane et al.; Yan et al.) of the same fields, implying the high fidelity of our selection. We crossmatch all high-z galaxy candidates presented in the five studies with our catalog and discuss the possible causes of discrepancy in the final lists.

RC100: Rotation Curves of 100 Massive Star-forming Galaxies at z = 0.6–2.5 Reveal Little Dark Matter on Galactic Scales

We analyze Hα or CO rotation curves extending out to several galaxy effective radii for 100 massive, large, star-forming disk galaxies (SFGs) across the peak of cosmic galaxy star formation (z ∼ 0.6–2.5), more than doubling the previous sample presented by Genzel et al. and Price et al. The observations were taken with SINFONI and KMOS integral-field spectrographs at the ESO-Very Large Telescope, LUCI-LBT, NOEMA-IRAM, and Atacama Large Millimeter/submillimeter Array. We fit the major-axis kinematics with beam-convolved, forward models of turbulent rotating disks with bulges embedded in dark matter (DM) halos, including the effects of pressure support. The fraction of dark to total matter within the disk effective radius (R e ∼ 5 kpc), f DM(R e) = V 2 DM(R e)/V 2 circ(R e) decreases with redshift: at z ∼ 1 (z ∼ 2) the median DM fraction is 0.38 ± 0.23 (0.27 ± 0.18), and a third (half) of all galaxies are maximal disks with f DM(R e) < 0.28. DM fractions correlate inversely with the baryonic surface density, and the low DM fractions can be explained with a flattened, or cored, inner DM density distribution. At z ∼ 2, there is ≈40% less DM mass on average within R e compared to expected values based on cosmological stellar-mass–halo-mass relations. The DM deficit is more evident at high star formation rate surface densities (≳2.5 M ⊙ yr−1 kpc2) and galaxies with massive bulges (≥1010 M ⊙). A combination of stellar or active galactic nucleus feedback, and/or heating due to dynamical friction, may drive the DM from cuspy into cored mass distributions, pointing to an efficient buildup of massive bulges and central black holes at z ∼ 2 SFGs.

Early Results from GLASS-JWST. VII. Evidence for Lensed, Gravitationally Bound Protoglobular Clusters at z = 4 in the Hubble Frontier Field A2744* *Based on observations collected with JWST under the ERS program 1324 (PI T. Treu).

We investigate the blue and optical rest-frame sizes (λ ≃ 2300–4000 Å) of three compact star-forming regions in a galaxy at z = 4 strongly lensed (×30, ×45, and ×100) by the Hubble Frontier Field galaxy cluster A2744 using GLASS-ERS James Webb Space Telescope (JWST)/NIRISS imaging at 1.15 μm, 1.50 μm, and 2.0 μm with a point-spread function ≲0.″1. In particular, the Balmer break is probed in detail for all multiply imaged sources of the system. With ages of a few tens of Myr, stellar masses in the range (0.7–4.0) ×106 M ⊙ and optical/ultraviolet effective radii spanning the interval 3 < R eff < 20 pc, such objects are currently the highest-redshift (spectroscopically confirmed) gravitationally bound young massive star clusters (YMCs), with stellar mass surface densities resembling those of local globular clusters. Optical (4000 Å, JWST-based) and ultraviolet (1600 Å, Hubble Space Telescope–based) sizes are fully compatible. The contribution to the ultraviolet underlying continuum emission (1600 Å) is ∼30%, which decreases by a factor of 2 in the optical for two of the YMCs (∼4000 Å rest-frame), reflecting the young ages (<30 Myr) inferred from the spectral energy distribution fitting and supported by the presence of high-ionization lines secured with the Very Large Telescope/MUSE. Such bursty forming regions enhance the specific star formation rate of the galaxy, which is ≃10 Gyr−1. This galaxy would be among the extreme analogs observed in the local universe having a high star formation rate surface density and a high occurrence of massive stellar clusters in formation.

Probing Cold Gas in a Massive, Compact Star-forming Galaxy at z = 6

Observations of low-order 12C16O transitions represent the most direct way to study galaxies’ cold molecular gas, the fuel of star formation. Here we present the first detection of CO(J = 2 → 1) in a galaxy lying on the main-sequence of star-forming galaxies at z > 6. Our target, G09-83808 at z = 6.03, has a short depletion timescale of τ dep ≈ 50 Myr and a relatively low gas fraction of M gas/M ⋆ ≈ 0.30 that contrasts with those measured for lower-redshift main-sequence galaxies. We conclude that this galaxy is undergoing a starburst episode with a high star formation efficiency that might be the result of gas compression within its compact rotating disk. Its starburst-like nature is further supported by its high star formation rate surface density, thus favoring the use of the Kennicutt–Schmidt relation as a more precise diagnostic diagram. Without further significant gas accretion, this galaxy would become a compact, massive quiescent galaxy at z ∼ 5.5. In addition, we find that the calibration for estimating interstellar medium masses from dust continuum emission satisfactorily reproduces the gas mass derived from the CO(2 → 1) transition (within a factor of ∼2). This is in line with previous studies claiming a small redshift evolution in the gas-to-dust ratio of massive, metal-rich galaxies. In the absence of gravitational amplification, this detection would have required of order 1000 hr of observing time. The detection of cold molecular gas in unlensed star-forming galaxies at high redshifts is thus prohibitive with current facilities and requires a tenfold improvement in sensitivity, such as that envisaged for the Next-Generation Very Large Array .

Physical Properties of Massive Compact Starburst Galaxies with Extreme Outflows

Abstract We present results on the nature of extreme ejective feedback episodes and the physical conditions of a population of massive (M * ∼ 1011 M ⊙), compact starburst galaxies at z = 0.4–0.7. We use data from Keck/NIRSPEC, SDSS, Gemini/GMOS, MMT, and Magellan/MagE to measure rest-frame optical and near-IR spectra of 14 starburst galaxies with extremely high star formation rate surface densities (mean ΣSFR ∼ 2000 M ⊙ yr−1 kpc−2) and powerful galactic outflows (maximum speeds v 98 ∼ 1000–3000 km s−1). Our unique data set includes an ensemble of both emission ([O ii] λλ3726,3729, Hβ, [O iii] λλ4959,5007, Hα, [N ii] λλ6549,6585, and [S ii] λλ6716,6731) and absorption (Mg ii λλ2796,2803, and Fe ii λ2586) lines that allow us to investigate the kinematics of the cool gas phase (T ∼ 104 K) in the outflows. Employing a suite of line ratio diagnostic diagrams, we find that the central starbursts are characterized by high electron densities (median n e ∼ 530 cm−3), and high metallicity (solar or supersolar). We show that the outflows are most likely driven by stellar feedback emerging from the extreme central starburst, rather than by an AGN. We also present multiple intriguing observational signatures suggesting that these galaxies may have substantial Lyman continuum (LyC) photon leakage, including weak [S ii] nebular emission lines. Our results imply that these galaxies may be captured in a short-lived phase of extreme star formation and feedback where much of their gas is violently blown out by powerful outflows that open up channels for LyC photons to escape.

The MALATANG survey: dense gas and star formation from high-transition HCN and HCO+ maps of NGC 253

ABSTRACT To study the high-transition dense-gas tracers and their relationships to the star formation of the inner ∼2 kpc circumnuclear region of NGC 253, we present HCN J = 4−3 and HCO+ J = 4−3 maps obtained with the James Clerk Maxwell Telescope. Using the spatially resolved data, we compute the concentration indices r90/r50 for the different tracers. HCN and HCO+ 4–3 emission features tend to be centrally concentrated, which is in contrast to the shallower distribution of CO 1–0 and the stellar component. The dense-gas fraction (fdense, traced by the velocity-integrated-intensity ratios of HCN/CO and HCO+/CO) and the ratio R31 (CO 3–2/1–0) decline towards larger galactocentric distances, but increase with higher star formation rate surface density. The radial variation and the large scatter of fdense and R31 imply distinct physical conditions in different regions of the galactic disc. The relationships of fdense versus Σstellar, and SFEdense versus Σstellar are explored. SFEdense increases with higher Σstellar in this galaxy, which is inconsistent with previous work that used HCN 1–0 data. This implies that existing stellar components might have different effects on the high-J HCN and HCO+ than their low-J emission. We also find that SFEdense seems to be decreasing with higher fdense which is consistent with previous works, and it suggests that the ability of the dense gas to form stars diminishes when the average density of the gas increases. This is expected in a scenario where only the regions with high-density contrast collapse and form stars.

From peculiar morphologies to Hubble-type spirals: the relation between galaxy dynamics and morphology in star-forming galaxies at z ∼ 1.5

ABSTRACT We present an analysis of the gas dynamics of star-forming galaxies at z ∼ 1.5 using data from the KMOS Galaxy Evolution Survey. We quantify the morphology of the galaxies using HSTcandels imaging parametrically and non-parametrically. We combine the H α dynamics from KMOS with the high-resolution imaging to derive the relation between stellar mass (M*) and stellar specific angular momentum (j*). We show that high-redshift star-forming galaxies at z ∼ 1.5 follow a power-law trend in specific stellar angular momentum with stellar mass similar to that of local late-type galaxies of the form j* ∝ M$_*^{0.53\, \pm \, 0.10}$. The highest specific angular momentum galaxies are mostly disc-like, although generally both peculiar morphologies and disc-like systems are found across the sequence of specific angular momentum at a fixed stellar mass. We explore the scatter within the j* – M* plane and its correlation with both the integrated dynamical properties of a galaxy (e.g. velocity dispersion, Toomre Qg, H α star formation rate surface density ΣSFR) and its parametrized rest-frame UV / optical morphology (e.g. Sérsic index, bulge to total ratio, clumpiness, asymmetry, and concentration). We establish that the position in the j* – M* plane is strongly correlated with the star-formation surface density and the clumpiness of the stellar light distribution. Galaxies with peculiar rest-frame UV / optical morphologies have comparable specific angular momentum to disc- dominated galaxies of the same stellar mass, but are clumpier and have higher star formation rate surface densities. We propose that the peculiar morphologies in high-redshift systems are driven by higher star formation rate surface densities and higher gas fractions leading to a more clumpy interstellar medium.

The Formation of Low-metallicity Globular Clusters in Dwarf Galaxy Mergers

We present a hydro-dynamical simulation at sub-parsec and few solar mass resolution of a merger between two gas-rich dwarf galaxies. Our simulation includes a detailed model for the multi-phase interstellar medium (ISM) and is able to follow the entire formation history of spatially resolved star clusters, including feedback from individual massive stars. Shortly after the merger we find a population of $\sim 900$ stellar clusters with masses above $10^{2.5}\; \rm{M_\odot}$ and a cluster mass function (CMF), which is well fitted with a power-law with a slope of $\alpha=-1.70\pm0.08$. We describe here in detail the formation of the three most massive clusters (M$_{*} \gtrsim 10^5$ M$_\odot$), which populate the high-mass end of the CMF. The simulated clusters form rapidly on a timescale of $6$-$8$ Myr in converging flows of dense gas. The embedded merger phase has extremely high star formation rate surface densities of $\Sigma_\mathrm{SFR}>10\; \mathrm{M}_\odot\; \mathrm{yr}^{-1}\; \mathrm{kpc}^{-2}$ and thermal gas pressures in excess of $P_{\rm th}\sim10^7 \; \mathrm{k}_{\rm B}\;(\rm K\;\mathrm{cm}^{-3})^{-1}$. The formation process is terminated by rapid gas expulsion driven by the first generation of supernovae, after which the cluster centers relax and both their structure and kinematics become indistinguishable from observed local globular clusters. The simulation presented here provides a general model for the formation of metal-poor globular clusters in chemically unevolved starbursting environments of low-mass dwarf galaxies, which are common at high redshifts.

Radio observations confirm young stellar populations in local analogues to z ∼ 5 Lyman break galaxies

We present radio observations at 1.5 GHz of 32 local objects selected to reproduce the physical properties of $z\sim5$ star-forming galaxies. We also report non-detections of five such sources in the sub-millimetre. We find a radio-derived star formation rate which is typically half that derived from H$\alpha$ emission for the same objects. These observations support previous indications that we are observing galaxies with a young dominant stellar population, which has not yet established a strong supernova-driven synchrotron continuum. We stress caution when applying star formation rate calibrations to stellar populations younger than 100 Myr. We calibrate the conversions for younger galaxies, which are dominated by a thermal radio emission component. We improve the size constraints for these sources, compared to previous unresolved ground-based optical observations. Their physical size limits indicate very high star formation rate surface densities, several orders of magnitude higher than the local galaxy population. In typical nearby galaxies, this would imply the presence of galaxy-wide winds. Given the young stellar populations, it is unclear whether a mechanism exists in our sources that can deposit sufficient kinetic energy into the interstellar medium to drive such outflows.

High Lyman Continuum Escape Fraction in a Lensed Young Compact Dwarf Galaxy at z = 2.5

Abstract We present the HST WFC3/F275W UV imaging observations of A2218-Flanking, a lensed compact dwarf galaxy at redshift . The stellar mass of A2218-Flanking is and SFR is yr−1 after correcting the magnification. This galaxy has a young galaxy age of 127 Myr and a compact galaxy size of . The HST UV imaging observations cover the rest-frame Lyman continuum (LyC) emission (∼800 Å) from A2218-Flanking. We firmly detect ( ) the LyC emission in A2218-Flanking in the F275W image. Together with the HST F606W images, we find that the absolute escape fraction of LyC is based on the flux density ratio between 1700 and 800 Å ( ). The morphology of the LyC emission in the F275W images is extended and follows the morphology of the UV continuum morphology in the F606W images, suggesting that the f 800 is not from foreground contaminants. We find that the region with a high star formation rate surface density has a lower (higher ) ratio than the diffused regions, suggesting that LyC photons are more likely to escape from the region with the intensive star-forming process. We compare the properties of galaxies with and without LyC detections and find that LyC photons are easier to escape in low-mass galaxies.

BULGE-FORMING GALAXIES WITH AN EXTENDED ROTATING DISK AT z ∼ 2

ABSTRACT We present 0.″2-resolution Atacama Large Millimeter/submillimeter Array observations at 870 μm for 25 Hα-seleced star-forming galaxies around the main sequence at z = 2.2–2.5. We detect significant 870 μm continuum emission in 16 (64%) of these galaxies. The high-resolution maps reveal that the dust emission is mostly radiated from a single region close to the galaxy center. Exploiting the visibility data taken over a wide uv distance range, we measure the half-light radii of the rest-frame far-infrared emission for the best sample of 12 massive galaxies with log(M */M ⊙) &gt; 11. We find nine galaxies to be associated with extremely compact dust emission with R 1/2,870 μm &lt; 1.5 kpc, which is more than a factor of 2 smaller than their rest-optical sizes, , and is comparable with optical sizes of massive quiescent galaxies at similar redshifts. As they have an exponential disk with Sérsic index of in the rest-optical, they are likely to be in the transition phase from extended disks to compact spheroids. Given their high star formation rate surface densities within the central 1 kpc of M ⊙ yr−1 kpc−2, the intense circumnuclear starbursts can rapidly build up a central bulge with ΣM *,1 kpc &gt; 1010 M ⊙ kpc−2 in several hundred megayears, i.e., by z ∼ 2. Moreover, ionized gas kinematics reveal that they are rotation supported with an angular momentum as large as that of typical star-forming galaxies at z = 1–3. Our results suggest that bulges are commonly formed in extended rotating disks by internal processes, not involving major mergers.

SXDF-ALMA 1.5 arcmin 2 DEEP SURVEY: A COMPACT DUSTY STAR-FORMING GALAXY AT z = 2.5

We present first results from the SXDF-ALMA 1.5 arcmin^2 deep survey at 1.1 mm using Atacama Large Millimeter Array (ALMA). The map reaches a 1sigma depth of 55 uJy/beam and covers 12 Halpha-selected star-forming galaxies at z = 2.19 or z=2.53. We have detected continuum emission from three of our Halpha-selected sample, including one compact star-forming galaxy with high stellar surface density, NB2315-07. They are all red in the rest-frame optical and have stellar masses of log (M*/Msun)>10.9 whereas the other blue, main-sequence galaxies with log(M*/Msun)=10.0-10.8 are exceedingly faint, <290 uJy (2sigma upper limit). We also find the 1.1 mm-brightest galaxy, NB2315-02, to be associated with a compact (R_e=0.7+-0.1 kpc), dusty star-forming component. Given high gas fraction (44^{+20}_{-8}% or 37^{+25}_{-3}%) and high star formation rate surface density (126^{+27}_{-30} Msun yr^{-1}kpc^{-2}), the concentrated starburst can within less than 50^{+12}_{-11} Myr build up a stellar surface density matching that of massive compact galaxies at z~2, provided at least 19+-3% of the total gas is converted into stars in the galaxy centre. On the other hand, NB2315-07, which already has such a high stellar surface density core, shows a gas fraction (23+-8%) and is located in the lower envelope of the star formation main-sequence. This compact less star-forming galaxy is likely to be in an intermediate phase between compact dusty star-forming and quiescent galaxies.

Metallicity and star formation activities of the interacting system Arp 86 from observations with MOS on the Xinglong 2.16 m telescope

We present an analysis of the metallicity and star formation activities of H II regions in the interacting system Arp 86, based on the first scientific observations using multi-object spectroscopy with the 2.16 m telescope at the Xinglong Observing Station. We find that the oxygen abundance gradient in Arp 86 is flatter than that in normal disk galaxies, which confirms that gas inflows caused by tidal forces during encounters can flatten the metallicity distributions in galaxies. The companion galaxy NGC 7752 is currently experiencing a galaxy-wide starburst with a higher star formation rate surface density than the main galaxy NGC 7753, which can be explained in that the companion galaxy is more susceptible to the effects of interaction than the primary. We also find that the galaxy 2MASX J23470758+2926531 has similar abundance and star formation properties to NGC 7753, and may be a part of the Arp 86 system.

HIGH RESOLUTION RADIO AND OPTICAL OBSERVATIONS OF THE CENTRAL STARBURST IN THE LOW-METALLICITY DWARF GALAXY II Zw 40

The extent to which star formation varies in galaxies with low masses, low metallicities, and high star formation rate surface densities is not well-constrained. To gain insight into star formation under these physical conditions, this paper estimates the ionizing photon fluxes, masses, and ages for young massive clusters in the central region of II Zw 40 -- the prototypical low-metallicity dwarf starburst galaxy -- from radio continuum and optical observations. Discrete, cluster-sized sources only account for half the total radio continuum emission; the remainder is diffuse. The young (<5 Myr) central burst has a star formation rate surface density that significantly exceeds that of the Milky Way. Three of the 13 sources have ionizing photon fluxes (and thus masses) greater than R136 in 30 Doradus. Although isolating the effects of galaxy mass and metallicity is difficult, the HII region luminosity function and the internal extinction in the center of II Zw 40 appear to be primarily driven by a merger-related starburst. The relatively flat HII region luminosity function may be the result of an increase in ISM pressure during the merger and the internal extinction is similar to that generated by the clumpy and porous dust in other starburst galaxies.

Metallicities and Physical Conditions in Star‐forming Galaxies atz∼ 1.0–1.51

We present a study of the mass-metallicity (M-Z) relation and H II region physical conditions in a sample of 20 star-forming galaxies at 1.0 < z < 1.5 drawn from the DEEP2 Galaxy Redshift Survey. We find a correlation between stellar mass and gas-phase oxygen abundance in the sample and compare it with the one observed among UV-selected z ∼ 2 star-forming galaxies and local objects from the Sloan Digital Sky Survey (SDSS). This comparison, based on the same empirical abundance indicator, demonstrates that the zero point of the M-Z relationship evolves with redshift, in the sense that galaxies at fixed stellar mass become more metal-rich at lower redshift. Measurements of [O III]/Hβ and [N II]/Hα emission-line ratios show that, on average, objects in the DEEP2 1.0 < z < 1.5 sample are significantly offset from the excitation sequence observed in nearby H II regions and SDSS emission-line galaxies. In order to fully understand the causes of this offset, which is also observed in z ∼ 2 star-forming galaxies, we examine in detail the small fraction of SDSS galaxies that have similar diagnostic ratios to those of the DEEP2 sample. Some of these galaxies indicate evidence for AGN and/or shock activity, which may give rise to their unusual line ratios and contribute to Balmer emission lines at the level of ~20%. Others indicate no evidence for AGN or shock excitation yet are characterized by higher electron densities and temperatures, and therefore interstellar gas pressures, than typical SDSS star-forming galaxies of similar stellar mass. These anomalous objects also have higher concentrations and starformation rate surface densities, which are directly connected to higher interstellar pressure. Higher star formation rate surface densities, interstellar pressures, and H II region ionization parameters may also be common at high redshift. These effects must be taken into account when using strong-line indicators to understand the evolution of heavy elements in galaxies. When such effects are included, the inferred evolution of the M-Z relation out to z ∼ 2 is more significant than previous estimates.