ALMA observations of the long wavelength dust continuum are used to estimate the interstellar medium (ISM) masses in a sample of 708 galaxies at z = 0.3 to 4.5 in the COSMOS field. The galaxy sample ...has known far-infrared luminosities and, hence, star formation rates (SFRs) and stellar masses ( ) from the optical-infrared spectrum fitting. The galaxies sample SFRs from the main sequence (MS) to 50 times above the MS. The derived ISM masses are used to determine the dependence of gas mass on redshift, , and specific SFR (sSFR) relative to the MS. The ISM masses increase approximately with the 0.63 power of the rate of increase in SFRs with redshift and the 0.32 power of the sSFR/sSFRMS. The SF efficiencies also increase as the 0.36 power of the SFR redshift evolution and the 0.7 power of the elevation above the MS; thus the increased activities at early epochs are driven by both increased ISM masses and SF efficiency. Using the derived ISM mass function, we estimate the accretion rates of gas required to maintain continuity of the MS evolution ( yr−1 at z > 2.5). Simple power-law dependencies are similarly derived for the gas accretion rates. We argue that the overall evolution of galaxies is driven by the rates of gas accretion. The cosmic evolution of total ISM mass is estimated and linked to the evolution of SF and active galactic nucleus activity at early epochs.
ALMA Resolves the Nuclear Disks of Arp 220 Scoville, Nick; Murchikova, Lena; Walter, Fabian ...
The Astrophysical journal,
02/2017, Letnik:
836, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present 90 mas (37 pc) resolution ALMA imaging of Arp 220 in the CO (1-0) line and continuum at . The internal gas distribution and kinematics of both galactic nuclei are well resolved for the ...first time. In the west nucleus, the major gas and dust emission extends out to 0 2 radius (74 pc); the central resolution element shows a strong peak in the dust emission but a factor of 3 dip in the CO line emission. In this nucleus, the dust is apparently optically thick ( ) at with a dust brightness temperature of ∼147 K. The column of interstellar matter at this nucleus is cm−2, corresponding to ∼900 gr cm−2. The east nucleus is more elongated with radial extent 0 3 or ∼111 pc. The derived kinematics of the nuclear disks provide a good fit to the line profiles, yielding the emissivity distributions, the rotation curves, and velocity dispersions. In the west nucleus, there is evidence of a central Keplerian component requiring a central mass of 8 × 108 . The intrinsic widths of the emission lines are (west) and 120 (east) km s−1. Given the very short dissipation timescales for turbulence ( 105 years), we suggest that the line widths may be due to semicoherent motions within the nuclear disks. The symmetry of the nuclear disk structures is impressive, implying the merger timescale is significantly longer than the rotation period of the disks.
Cosmic Evolution of Gas and Star Formation Scoville, Nick; Faisst, Andreas; Weaver, John ...
The Astrophysical journal,
02/2023, Letnik:
943, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
Atacama Large Millimeter/submillimeter Array (ALMA) observations of the long-wavelength dust continuum are used to estimate the gas masses in a sample of 708 star-forming galaxies at
z
= ...0.3−4.5. We determine the dependence of gas masses and star formation efficiencies (SFEs; SFR per unit gas mass) on redshift (z),
M
*
, and star formation rate (SFR) relative to the main sequence (MS). We find that 70% of the increase in SFRs of the MS is due to the increased gas masses at earlier epochs, while 30% is due to increased efficiency of star formation (SF). For galaxies above the MS this is reversed—with 70% of the increased SFR relative to the MS being due to elevated SFEs. Thus, the major evolution of star formation activity at early epochs is driven by increased gas masses, while the starburst activity taking galaxies above the MS is due to enhanced triggering of star formation (likely due to galactic merging). The interstellar gas peaks at
z
= 2 and dominates the stellar mass down to
z
= 1.2. Accretion rates needed to maintain continuity of the MS evolution reach >100
M
⊙
yr
−1
at
z
> 2. The galactic gas contents are likely the driving determinant for both the rise in SF and AGN activity from
z
= 5 to their peak at
z
= 2 and subsequent fall at lower
z
. We suggest that for self-gravitating clouds with supersonic turbulence, cloud collisions and the filamentary structure of the clouds regulate the star formation activity.
We present new subarcsecond-resolution Karl G. Jansky Very Large Array (VLA) imaging at 10 GHz of 155 ultraluminous (Lbol ∼ 1011.7-1014.2 L ) and heavily obscured quasars with redshifts z ∼ 0.4-3. ...The sample was selected to have extremely red mid-infrared-optical color ratios based on data from the Wide-Field Infrared Survey Explorer (WISE) along with a detection of bright, unresolved radio emission from the NRAO VLA Sky Survey (NVSS) or Faint Images of the Radio Sky at Twenty cm Survey. Our high-resolution VLA observations have revealed that the majority of the sources in our sample (93 out of 155) are compact on angular scales <0 2 (≤1.7 kpc at z ∼ 2). The radio luminosities, linear extents, and lobe pressures of our sources are similar to young radio active galactic nuclei (e.g., gigahertz-peaked spectrum GPS and compact steep-spectrum CSS sources), but their space density is considerably lower. Application of a simple adiabatic lobe expansion model suggests relatively young dynamical ages (∼104-7 yr), relatively high ambient ISM densities (∼1-104 cm−3), and modest lobe expansion speeds (∼30-10,000 km s−1). Thus, we find our sources to be consistent with a population of newly triggered, young jets caught in a unique evolutionary stage in which they still reside within the dense gas reservoirs of their hosts. Based on their radio luminosity function and dynamical ages, we estimate that only ∼20% of classical large-scale FR I/II radio galaxies could have evolved directly from these objects. We speculate that the WISE-NVSS sources might first become GPS or CSS sources, of which some might ultimately evolve into larger radio galaxies.
Abstract
The Herschel Space Observatory has revealed a very different galaxyscape from that shown by optical surveys which presents a challenge for galaxy-evolution models. The Herschel surveys ...reveal (1) that there was rapid galaxy evolution in the very recent past and (2) that galaxies lie on a single Galaxy Sequence (GS) rather than a star-forming ‘main sequence’ and a separate region of ‘passive’ or ‘red-and-dead’ galaxies. The form of the GS is now clearer because far-infrared surveys such as the Herschel ATLAS pick up a population of optically red star-forming galaxies that would have been classified as passive using most optical criteria. The space-density of this population is at least as high as the traditional star-forming population. By stacking spectra of H-ATLAS galaxies over the redshift range 0.001 < z < 0.4, we show that the galaxies responsible for the rapid low-redshift evolution have high stellar masses, high star-formation rates but, even several billion years in the past, old stellar populations – they are thus likely to be relatively recent ancestors of early-type galaxies in the Universe today. The form of the GS is inconsistent with rapid quenching models and neither the analytic bathtub model nor the hydrodynamical EAGLE simulation can reproduce the rapid cosmic evolution. We propose a new gentler model of galaxy evolution that can explain the new Herschel results and other key properties of the galaxy population.
We present new results from the Submillimetre Common-User Bolometer Array (SCUBA) Local Universe Galaxy Survey (SLUGS), the first large systematic submillimetre (submm) survey of the local Universe. ...Since our initial survey of a sample of 104 IRAS-selected galaxies we have now completed a survey of a sample of 81 optically selected galaxies, observed with the SCUBA camera on the James Clerk Maxwell Telescope. Since SCUBA is sensitive to the 90 per cent of dust too cold to radiate significantly in the IRAS bands our new sample represents the first unbiased SCUBA survey of dust in galaxies along the whole length of the Hubble sequence. We find little change in the properties of dust in galaxies along the Hubble sequence, except a marginally significant trend for early-type galaxies to be less-luminous submm sources than late types. We nevertheless detected six out of 11 elliptical galaxies, although some of the emission may possibly be synchrotron rather than dust emission. As in our earlier work on IRAS galaxies we find that the IRAS and submm fluxes are well fitted by a two-component dust model with dust emissivity index β= 2. The major difference from our earlier work is that we find the ratio of the mass of cold dust to the mass of warm dust is much higher for our optically selected galaxies and can reach values of ∼1000. Comparison of the results for the IRAS and optically selected samples shows that there is a population of galaxies containing a large proportion of cold dust that is unrepresented in the IRAS sample. We derive local submm luminosity and dust mass functions, both directly from our optically selected SLUGS sample, and by extrapolation from the IRAS Point Source Catalogue Redshift Survey (PSCz) survey using the method of Serjeant and Harrison (by extrapolating the spectral energy distributions of the IRAS PSCz survey galaxies out to 850 μm we probe a wider range of luminosities than probed directly by the SLUGS samples), and find excellent agreement between the two. We find them to be well fitted by Schechter functions except at the highest luminosities. We find that as a consequence of the omission of cold galaxies from the IRAS sample the luminosity function presented in our earlier work is too low by a factor of 2, reducing the amount of cosmic evolution required between the low-z and high-z Universe.
We present millimeter- and submillimeter-wave phase characteristics measured between 2012 and 2014 of Atacama Large Millimeter/submillimeter Array long baseline campaigns. This paper presents the ...first detailed investigation of the characteristics of phase fluctuation and phase correction methods obtained with baseline lengths up to ∼15 km. The basic phase fluctuation characteristics can be expressed with the spatial structure function (SSF). Most of the SSFs show that the phase fluctuation increases as a function of baseline length, with a power-law slope of ∼0.6. In many cases, we find that the slope becomes shallower (average of ∼0.2-0.3) at baseline lengths longer than ∼1 km, namely showing a turn-over in SSF. These power law slopes do not change with the amount of precipitable water vapor (PWV), but the fitted constants have a weak correlation with PWV, so that the phase fluctuation at a baseline length of 10 km also increases as a function of PWV. The phase correction method using water vapor radiometers (WVRs) works well, especially for the cases where PWV > 1 mm , which reduces the degree of phase fluctuations by a factor of two in many cases. However, phase fluctuations still remain after the WVR phase correction, suggesting the existence of other turbulent constituent that cause the phase fluctuation. This is supported by occasional SSFs that do not exhibit any turn-over; these are only seen when the PWV is low (i.e., when the WVR phase correction works less effectively) or after WVR phase correction. This means that the phase fluctuation caused by this turbulent constituent is inherently smaller than that caused by water vapor. Since in these rare cases there is no turn-over in the SSF up to the maximum baseline length of ∼15 km, this turbulent constituent must have scale height of 10 km or more, and thus cannot be water vapor, whose scale height is around 1 km. Based on the characteristics, this large scale height turbulent constituent is likely to be water ice or a dry component. Excess path length fluctuation after the WVR phase correction at a baseline length of 10 km is large ( 200 m ), which is significant for high frequency ( > 450 GHz or < 700 m ) observations. These results suggest the need for an additional phase correction method to reduce the degree of phase fluctuation, such as fast switching, in addition to the WVR phase correction. We simulated the fast switching phase correction method using observations of single quasars, and the result suggests that it works well, with shorter cycle times linearly improving the coherence.
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