We present ALMA Band 9 observations of the C II158 μm emission for a sample of 10 main-sequence galaxies at redshift z ˜ 2, with typical stellar masses (log M⋆/M⊙ ˜ 10.0-10.9) and star formation ...rates (˜35-115 M⊙ yr-1). Given the strong and well-understood evolution of the interstellar medium from the present to z = 2, we investigate the behaviour of the C II emission and empirically identify its primary driver. We detect C II from six galaxies (four secure and two tentative) and estimate ensemble averages including non-detections. The C II-to-infrared luminosity ratio (C II/LIR) of our sample is similar to that of local main-sequence galaxies (˜2 × 10-3), and ˜10 times higher than that of starbursts. The C II emission has an average spatial extent of 4-7 kpc, consistent with the optical size. Complementing our sample with literature data, we find that the C II luminosity correlates with galaxies' molecular gas mass, with a mean absolute deviation of 0.2 dex and without evident systematics: the C II-to-H2 conversion factor (α _C II ˜ 30 M⊙/L⊙) is largely independent of galaxies' depletion time, metallicity, and redshift. C II seems therefore a convenient tracer to estimate galaxies' molecular gas content regardless of their starburst or main-sequence nature, and extending to metal-poor galaxies at low and high redshifts. The dearth of C II emission reported for z > 6-7 galaxies might suggest either a high star formation efficiency or a small fraction of ultraviolet light from star formation reprocessed by dust.
Aims. We use high-resolution continuum images obtained with the Atacama Large Millimeter Array (ALMA) to probe the surface density of star formation in z ~ 2 galaxies and study the different physical ...properties between galaxies within and above the star-formation main sequence of galaxies. Methods. We use ALMA images at 870 μm with 0.2 arcsec resolution in order to resolve star formation in a sample of eight star-forming galaxies at z ~ 2 selected among the most massive Herschel galaxies in the GOODS-South field. This sample is supplemented with eleven galaxies from the public data of the 1.3 mm survey of the Hubble Ultra-Deep Field, HUDF. We derive dust and gas masses for the galaxies, compute their depletion times and gas fractions, and study the relative distributions of rest-frame ultraviolet (UV) and far-infrared (FIR) light. Results. ALMA reveals systematically dense concentrations of dusty star formation close to the center of the stellar component of the galaxies. We identify two different starburst regimes: (i) the classical population of starbursts located above the SFR-M⋆ main sequence, with enhanced gas fractions and short depletion times and (ii) a sub-population of galaxies located within the scatter of the main sequence that experience compact star formation with depletion timescales typical of starbursts of ~150 Myr. In both starburst populations, the FIR and UV are distributed in distinct regions and dust-corrected star formation rates (SFRs) estimated using UV-optical-near-infrared data alone underestimate the total SFR. Starbursts hidden in the main sequence show instead the lowest gas fractions of our sample and could represent the last stage of star formation prior to passivization. Being Herschel-selected, these main sequence galaxies are located in the high-mass end of the main sequence, hence we do not know whether these “starbursts hidden in the main sequence” also exist below 1011 M⊙. Active galactic nuclei (AGNs) are found to be ubiquitous in these compact starbursts, suggesting that the triggering mechanism also feeds the central black hole or that the active nucleus triggers star formation.
Giant star-forming clumps? Ivison, R J; Richard, J; Biggs, A D ...
Monthly notices of the Royal Astronomical Society. Letters,
06/2020, Letnik:
495, Številka:
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ABSTRACT
With the spatial resolution of the Atacama Large Millimetre Array (ALMA), dusty galaxies in the distant Universe typically appear as single, compact blobs of dust emission, with a median ...half-light radius, ≈1 kpc. Occasionally, strong gravitational lensing by foreground galaxies or galaxy clusters has probed spatial scales 1–2 orders of magnitude smaller, often revealing late-stage mergers, sometimes with tantalizing hints of sub-structure. One lensed galaxy in particular, the Cosmic Eyelash at z = 2.3, has been cited extensively as an example of where the interstellar medium exhibits obvious, pronounced clumps, on a spatial scale of ≈100 pc. Seven orders of magnitude more luminous than giant molecular clouds in the local Universe, these features are presented as circumstantial evidence that the blue clumps observed in many z ∼ 2–3 galaxies are important sites of ongoing star formation, with significant masses of gas and stars. Here, we present data from ALMA which reveal that the dust continuum of the Cosmic Eyelash is in fact smooth and can be reproduced using two Sérsic profiles with effective radii, 1.2 and 4.4 kpc, with no evidence of significant star-forming clumps down to a spatial scale of ≈80 pc and a star formation rate of <3 M⊙ yr−1.
Abstract
We present the results of a new study of the relationship between infrared excess (IRX ≡ LIR/LUV), ultraviolet (UV) spectral slope (β) and stellar mass at redshifts 2 < z < 3, based on a ...deep Atacama Large Millimeter Array (ALMA) 1.3-mm continuum mosaic of the Hubble Ultra Deep Field. Excluding the most heavily obscured sources, we use a stacking analysis to show that z ≃ 2.5 star-forming galaxies in the mass range $9.25\le \log (M_{\ast }/\rm M_{{\odot }}) \le 10.75$ are fully consistent with the IRX–β relation expected for a relatively grey attenuation curve, similar to the commonly adopted Calzetti law. Based on a large, mass-complete sample of 2 ≤ z ≤ 3 star-forming galaxies drawn from multiple surveys, we proceed to derive a new empirical relationship between β and stellar mass, making it possible to predict UV attenuation (A1600) and IRX as a function of stellar mass, for any assumed attenuation law. Once again, we find that z ≃ 2.5 star-forming galaxies follow A1600–M* and IRX–M* relations consistent with a relatively grey attenuation law, and find no compelling evidence that star-forming galaxies at this epoch follow a reddening law as steep as the Small Magellanic Cloud (SMC) extinction curve. In fact, we use a simple simulation to demonstrate that previous determinations of the IRX–β relation may have been biased towards low values of IRX at red values of β, mimicking the signature expected for an SMC-like dust law. We show that this provides a plausible mechanism for reconciling apparently contradictory results in the literature and that, based on typical measurement uncertainties, stellar mass provides a cleaner prediction of UV attenuation than β. Although the situation at lower stellar masses remains uncertain, we conclude that for 2 < z < 3 star-forming galaxies with $\log (M_{\ast }/\rm M_{{\odot }}) \ge 9.75$, both the IRX–β and IRX–M* relations are well described by a Calzetti-like attenuation law.
We present high-fidelity, 30 mas (200 pc) resolution ALMA rest-frame 240 m observations of cold dust emission in three typical main-sequence star-forming galaxies (SFGs) at z ∼ 3 in the Hubble ...Ultra-Deep Field (HUDF). The cold dust is distributed within the smooth disklike central regions of star formation 1-3 kpc in diameter, despite their complex and disturbed rest-frame UV and optical morphologies. No dust substructures or clumps are seen down to 1-3 yr−1 (1 ) per 200 pc beam. No dust emission is observed at the locations of UV-emitting clumps, which lie 2-10 kpc from the bulk of star formation. Clumpy substructures can contribute no more than 1%-7% of the total star formation in these galaxies (3 upper limits). The lack of star-forming substructures in our HUDF galaxies is to be contrasted with the multiple substructures characteristic of submillimeter-selected galaxies (SMGs) at the same cosmic epoch, particularly the far-IR-bright SMGs with similarly high-fidelity ALMA observations of Hodge et al. Individual star-forming substructures in these SMGs contain ∼10%-30% of their total star formation. A substructure in these SMGs is often comparably bright in the far-infrared to (or in some cases brighter than) our typical SFGs, suggesting that these SMGs originate from a class of disruptive events involving multiple objects at the scale of our HUDF galaxies. The scale of the disruptive event found in our main-sequence SFGs, characterized by the lack of star-forming substructures at our resolution and sensitivity, could be less violent, e.g., gas-rich disk instability or minor mergers.
Abstract
Similarly to the cosmic star formation history, the black hole accretion rate density of the Universe peaked at 1 < z < 3. This cosmic epoch is hence best suited for investigating the ...effects of radiative feedback from active galactic nucleus (AGN). Observational efforts are under way to quantify the impact of the AGN feedback, if any, on their host galaxies. Here, we present a study of the molecular gas content of AGN hosts at z ∼ 1.5 using CO2−1 line emission observed with Atacama Large Millimeter/sub-mm Array (ALMA) for a sample of 10 AGNs. We compare this with a sample of galaxies without an AGN matched in redshift, stellar mass and star formation rate. We detect CO in three AGNs with L
CO ∼ 6.3–25.1 × 109 L⊙, which translates to a molecular hydrogen gas mass of 2.5–10 × 1010 M⊙ assuming conventional conversion factor of αCO ∼ 3.6. Our results indicate a >99 per cent probability of lower depletion time-scales and lower molecular gas fractions in AGN hosts with respect to the non-AGN comparison sample. We discuss the implications of these observations on the impact that AGN feedback may have on star formation efficiency of z >1 galaxies.
We present high spatial resolution (FWHM ∼ 0 14) observations of the CO(8-7) line in GDS-14876, a compact star-forming galaxy at z = 2.3 with a total stellar mass of log(M /M ) = 10.9. The spatially ...resolved velocity map of the inner r 1 kpc reveals a continuous velocity gradient consistent with the kinematics of a rotating disk with vrot(r = 1 kpc) = 163 5 km s−1 and vrot/ ∼ 2.5. The gas-to-stellar ratios estimated from CO(8-7) and the dust continuum emission span a broad range, and , but are nonetheless consistent given the uncertainties in the conversion factors. The dynamical modeling yields a dynamical mass of , which is lower, but still consistent with the baryonic mass, , if the smallest CO-based gas fraction is assumed. Despite a low, overall gas fraction, the small physical extent of the dense, star-forming gas probed by CO(8-7), ∼3× smaller than the stellar size, implies a strong relative concentration that increases the gas fraction up to in the central 1 kpc. Such a gas-rich center, coupled with a high star formation rate (SFR) ∼ 500 M yr−1, suggests that GDS-14876 is quickly assembling a dense stellar component (bulge) in a strong nuclear starburst. Assuming its gas reservoir is depleted without replenishment, GDS-14876 will quickly (tdepl ∼ 27 Myr) become a compact quiescent galaxy that could retain some fraction of the observed rotational support.
A deep ALMA image of the Hubble Ultra Deep Field Dunlop, J. S; McLure, R. J; Biggs, A. D ...
Monthly notices of the Royal Astronomical Society,
04/2017, Letnik:
466, Številka:
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We present the results of the first, deep Atacama Large Millimeter Array (ALMA) imaging covering the full ≃4.5 arcmin2 of the Hubble Ultra Deep Field (HUDF) imaged with Wide Field Camera ...3/IR on HST. Using a 45-pointing mosaic, we have obtained a homogeneous 1.3-mm image reaching σ1.3 ≃ 35 μJy, at a resolution of ≃0.7 arcsec. From an initial list of ≃50 > 3.5σ peaks, a rigorous analysis confirms 16 sources with S
1.3 > 120 μJy. All of these have secure galaxy counterparts with robust redshifts (〈z〉 = 2.15). Due to the unparalleled supporting data, the physical properties of the ALMA sources are well constrained, including their stellar masses (M
*) and UV+FIR star formation rates (SFR). Our results show that stellar mass is the best predictor of SFR in the high-redshift Universe; indeed at z ≥ 2 our ALMA sample contains seven of the nine galaxies in the HUDF with M
* ≥ 2 × 1010 M⊙, and we detect only one galaxy at z > 3.5, reflecting the rapid drop-off of high-mass galaxies with increasing redshift. The detections, coupled with stacking, allow us to probe the redshift/mass distribution of the 1.3-mm background down to S
1.3 ≃ 10 μJy. We find strong evidence for a steep star-forming ‘main sequence’ at z ≃ 2, with SFR ∝M
* and a mean specific SFR ≃ 2.2 Gyr−1. Moreover, we find that ≃85 per cent of total star formation at z ≃ 2 is enshrouded in dust, with ≃65 per cent of all star formation at this epoch occurring in high-mass galaxies (M
* > 2 × 1010 M⊙), for which the average obscured:unobscured SF ratio is ≃200. Finally, we revisit the cosmic evolution of SFR density; we find this peaks at z ≃ 2.5, and that the star-forming Universe transits from primarily unobscured to primarily obscured at z ≃ 4.
The most dramatic phases of terrestrial planet formation are thought to be oligarchic and chaotic growth, on timescales of up to 100-200 Myr, when violent impacts occur between large planetesimals of ...sizes up to protoplanets. Such events are marked by the production of large amounts of debris, as has been observed in some exceptionally bright and young debris disks (termed extreme debris disks). Here we report five years of Spitzer measurements of such systems around two young solar-type stars: ID8 and P1121. The short-term (weekly to monthly) and long-term (yearly) disk variability is consistent with the aftermaths of large impacts involving large asteroid-sized bodies. We demonstrate that an impact-produced clump of optically thick dust, under the influence of the dynamical and viewing geometry effects, can produce short-term modulation in the disk light curves. The long-term disk flux variation is related to the collisional evolution within the impact-produced fragments once released into a circumstellar orbit. The time-variable behavior observed in the P1121 system is consistent with a hypervelocity impact prior to 2012 that produced vapor condensates as the dominant impact product. Two distinct short-term modulations in the ID8 system suggest two violent impacts at different times and locations. Its long-term variation is consistent with the collisional evolution of two different populations of impact-produced debris dominated by either vapor condensates or escaping boulders. The bright, variable emission from the dust produced in large impacts from extreme debris disks provides a unique opportunity to study violent events during the era of terrestrial planet formation.
Energetic feedback by active galactic nuclei (AGNs) plays an important evolutionary role in the regulation of star formation on galactic scales. However, the effects of this feedback as a function of ...redshift and galaxy properties such as mass, environment, and cold gas content remain poorly understood. The broad frequency coverage (1 to 116 GHz), high sensitivity (up to ten times higher than the Karl G. Jansky Very Large Array), and superb angular resolution (maximum baselines of at least a few hundred kilometers) of the proposed next-generation Very Large Array (ngVLA) are uniquely poised to revolutionize our understanding of AGNs and their role in galaxy evolution. Here, we provide an overview of the science related to AGN feedback that will be possible in the ngVLA era and present new continuum ngVLA imaging simulations of resolved radio jets spanning a wide range of intrinsic extents. We also consider key computational challenges and discuss exciting opportunities for multiwavelength synergy with other next-generation instruments, such as the Square Kilometer Array and the James Webb Space Telescope. The unique combination of high-resolution, large collecting area, and wide frequency range will enable significant advancements in our understanding of the effects of jet-driven feedback on sub-galactic scales, particularly for sources with extents of a few parsec to a few kiloparsec, such as young and/or lower-power radio AGNs, AGNs hosted by low-mass galaxies, radio jets that are interacting strongly with the interstellar medium of the host galaxy, and AGNs at high redshift.
![The [C ii] emission as a mo...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0035-8711/small "The [C ii] emission as a molecular gas mass tracer in galaxies at low and high redshifts")
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