The cosmic history of hot gas cooling and radio active galactic nucleus activity in massive early-type galaxies

We study the X-ray properties of 393 optically selected early-type galaxies (ETGs) over the redshift range of z≈ 0.0–1.2 in the Chandra Deep Fields (CDFs). To measure the average X-ray properties of the ETG population, we use X-ray stacking analyses with a subset of 158 passive ETGs (148 of which were individually undetected in X-ray). This ETG subset was constructed to span the redshift ranges of z= 0.1–1.2 in the ≈4 Ms CDF-South and ≈2 Ms CDF-North and z= 0.1–0.6 in the ≈250 ks Extended-CDF-South where the contribution from individually undetected active galactic nuclei (AGN) is expected to be negligible in our stacking. We find that 55 of the ETGs are detected individually in X-ray, and 12 of these galaxies have properties consistent with being passive hot-gas-dominated systems (i.e. systems not dominated by an X-ray bright AGN). On the basis of our analyses, we find little evolution in the mean 0.5–2 keV to B-band luminosity ratio (LX/LB∝ [1 +z]1.2) since z≈ 1.2, implying that some heating mechanism prevents the gas from cooling in these systems. We consider that feedback from radio-mode AGN activity could be responsible for heating the gas. We select radio AGN in the ETG population using their far-infrared/radio flux ratio. Our radio observations allow us to constrain the duty cycle history of radio AGN activity in our ETG sample. We estimate that if scaling relations between radio and mechanical power hold out to z≈ 1.2 for the ETG population being studied here, the average mechanical power from AGN activity is a factor of ≈1.4–2.6 times larger than the average radiative cooling power from hot gas over the redshift range z≈ 0–1.2. The excess of inferred AGN mechanical power from these ETGs is consistent with that found in the local Universe for similar types of galaxies

13CO and C18O emission from a dense gas disc at z = 2.3: abundance variations, cosmic rays and the initial conditions for star formation

We analyse the spectral line energy distributions of 13CO and C18O for the J = 1→0 up to J = 7→6 transitions in the gravitationally lensed ultraluminous infrared galaxy SMM J2135−0102 at z = 2.3. This is the first detection of 13CO and C18O in a high-redshift star-forming galaxy. These data comprise observations of six transitions taken with Plateau de Bure Interferometer and we combine these with ∼33 GHz Jansky Very Large Array data and our previous spatially resolved 12CO and continuum emission information to better constrain the properties of the interstellar medium (ISM) within this system. We study both the velocity-integrated and kinematically decomposed properties of the galaxy and coupled with a large velocity gradient (LVG) model we find that the star-forming regions in the system vary in their cold gas properties, in particular in their chemical abundance ratios. We find strong C18O emission both in the velocity-integrated emission and in the two kinematic components at the periphery of the system, where the C18O line flux is equivalent to or higher than the 13CO. We derive an average velocity-integrated flux ratio of 13CO/C18O ∼ 1 which suggests an abundance ratio of [13CO]/[C18O] which is at least seven times lower than that in the Milky Way. This is suggestive of enhanced C18O abundance, perhaps indicating star formation preferentially biased to high-mass stars. We estimate the relative contribution to the ISM heating from cosmic rays and UV of (30–3300) × 10−25 erg s−1 and 45 × 10−25 erg s−1 per H2 molecule respectively and find them to be comparable to the total cooling rate of (0.8–20) × 10−25 erg s−1 from the CO. However, our LVG models indicate high (>100 K) temperatures and densities (>103) cm−3 in the ISM which may suggest that cosmic rays play a more important role than UV heating in this system. If cosmic rays dominate the heating of the ISM, the increased temperature in the star-forming regions may favour the formation of massive stars and so explain the enhanced C18O abundance. This is a potentially important result for a system which may evolve into a local elliptical galaxy

An ALMA Survey of Submillimeter Galaxies in the Extended Chandra Deep Field-South: The AGN Fraction and X-Ray Properties of Submillimeter Galaxies

The large gas and dust reservoirs of submillimeter galaxies (SMGs) could potentially provide ample fuel to trigger an active galactic nucleus (AGN), but previous studies of the AGN fraction in SMGs have been controversial largely due to the inhomogeneity and limited angular resolution of the available submillimeter surveys. Here we set improved constraints on the AGN fraction and X-ray properties of the SMGs with Atacama Large Millimeter/submillimeter Array (ALMA) and Chandra observations in the Extended Chandra Deep Field-South (E-CDF-S). This study is the first among similar works to have unambiguously identified the X-ray counterparts of SMGs; this is accomplished using the fully submillimeter-identified, statistically reliable SMG catalog with 99 SMGs from the ALMA LABOCA E-CDF-S Submillimeter Survey. We found 10 X-ray sources associated with SMGs (median redshift z = 2.3), of which eight were identified as AGNs using several techniques that enable cross-checking. The other two X-ray detected SMGs have levels of X-ray emission that can be plausibly explained by their star formation activity. Six of the eight SMG-AGNs are moderately/highly absorbed, with N H > 1023 cm?2. An analysis of the AGN fraction, taking into account the spatial variation of X-ray sensitivity, yields an AGN fraction of $17^{+16}_{-6}\%$ for AGNs with rest-frame 0.5-8?keV absorption-corrected luminosity ?7.8 × 1042?erg?s?1; we provide estimated AGN fractions as a function of X-ray flux and luminosity. ALMA's high angular resolution also enables direct X-ray stacking at the precise positions of SMGs for the first time, and we found four potential SMG-AGNs in our stacking sample

An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field-South: detection of [C II] at z = 4.4

We present Atacama Large Millimeter Array (ALMA) 870-μm (345-GHz) observations of two submillimetre galaxies (SMGs) drawn from an ALMA study of the 126 submillimetre sources from the LABOCA Extended Chandra Deep Field-South Survey (LESS). The ALMA data identify the counterparts to these previously unidentified submillimetre sources and serendipitously detect bright emission lines in their spectra which we show are most likely to be [CII] 157.74 μm emission yielding redshifts of z = 4.42 and 4.44. This blind detection rate within the 7.5-GHz bandpass of ALMA is consistent with the previously derived photometric redshift distribution of SMGs and suggests a modest, but not dominant (≲25 per cent), tail of 870-μm selected SMGs at z ≳ 4. We find that the ratio of L[C II]/LFIR in these SMGs is much higher than seen for similarly far-infrared-luminous galaxies at z ˜ 0, which is attributed to the more extended gas reservoirs in these high-redshift ultraluminous infrared galaxies (ULIRGs). Indeed, in one system we show that the [C II] emission shows hints of extended emission on ≳ 3 kpc scales. Finally, we use the volume probed by our ALMA survey to show that the bright end of the [C II] luminosity function evolves strongly between z = 0 and ˜4.4, reflecting the increased interstellar medium cooling in galaxies as a result of their higher star formation rates. These observations demonstrate that even with short integrations, ALMA is able to detect the dominant fine-structure cooling lines from high-redshift ULIRGs, measure their energetics and spatially resolved properties and trace their evolution with redshift

The SCUBA-2 Cosmology Legacy Survey: Ultraluminous star-forming galaxies in a z=1.6 cluster

We analyze new SCUBA-2 submillimeter and archival SPIRE far-infrared imaging of a z = 1.62 cluster, Cl 0218.3–0510, which lies in the UKIRT Infrared Deep Sky Survey/Ultra-Deep Survey field of the SCUBA-2 Cosmology Legacy Survey. Combining these tracers of obscured star-formation activity with the extensive photometric and spectroscopic information available for this field, we identify 31 far-infrared/submillimeter-detected probable cluster members with bolometric luminosities 1012 L ☉ and show that by virtue of their dust content and activity, these represent some of the reddest and brightest galaxies in this structure. We exploit ALMA submillimeter continuum observations, which cover one of these sources, to confirm the identification of a SCUBA-2-detected ultraluminous star-forming galaxy in this structure. Integrating the total star-formation activity in the central region of the structure, we estimate that it is an order of magnitude higher (in a mass-normalized sense) than clusters at z ~ 0.5-1. However, we also find that the most active cluster members do not reside in the densest regions of the structure, which instead host a population of passive and massive, red galaxies. We suggest that while the passive and active populations have comparable near-infrared luminosities at z = 1.6, MH ~ –23, the subsequent stronger fading of the more active galaxies means that they will evolve into passive systems at the present day that are less luminous than the descendants of those galaxies that were already passive at z ~ 1.6 (MH ~ –20.5 and MH ~ –21.5, respectively, at z ~ 0). We conclude that the massive galaxy population in the dense cores of present-day clusters were already in place at z = 1.6 and that in Cl 0218.3–0510 we are seeing continuing infall of less extreme, but still ultraluminous, star-forming galaxies onto a pre-existing structure

Tracing cool molecular gas and star formation on ∼100 pc scales within a z ∼ 2.3 galaxy

We present new, high-angular resolution interferometric observations with the Karl G. Jansky Very Large Array of 12CO J = 1−0 line emission and 4–8 GHz continuum emission in the strongly lensed, z = 2.3 submillimetre galaxy, SMM J21352-0102. Using these data, we identify and probe the conditions in ∼100 pc clumps within this galaxy, which we consider to be potential giant molecular cloud complexes, containing up to half of the total molecular gas in this system. In combination with far-infrared and submillimetre data, we investigate the far-infrared/radio correlation, measuring qIR = 2.39 ± 0.17 across SMM J21352. We search for variations in the properties of the interstellar medium (ISM) throughout the galaxy by measuring the spatially resolved qIR and radio spectral index, αradio, finding ranges qIR =[2.1, 2.6] and αradio = [−1.5, −0.7]. We argue that these ranges in αradio and qIR may reflect variations in the age of the ISM material. Using multi-J 12CO data, we quantitatively test a recent theoretical model relating the star formation rate surface density to the excitation of 12CO, finding good agreement between the model and the data. Lastly, we study the Schmidt–Kennicutt relation, both integrated across the system and within the individual clumps. We find small offsets between SMM J21352 and its clumps relative to other star-forming galaxy populations on the Schmidt–Kennicutt plot – such offsets have previously been interpreted as evidence for a bi-modal star formation law, but we argue that they can be equally well explained as arising due to a combination of observational uncertainties and systematic biases in the choice of model used to interpret the data

Using [C I] to probe the interstellar medium in z ∼ 2.5 sub-millimeter galaxies

We present new [C I](1–0) and 12CO(4–3) Plateau de Bure Interferometer observations of five sub-millimeter galaxies (SMGs) and combine these with all available [C I](1–0) literature detections in SMGs to probe the gas distribution within a sample of 14 systems. We explore the [C I](1–0) properties of the SMG population, particularly investigating the ratio of the [C I](1–0) luminosity to various 12CO transition and far-infrared luminosities. We find that the SMGs with new observations extend the spread of L[CI](1-0)/LFIR to much higher values than found before, with our complete sample providing a good representation of the diverse z > 2 SMG population. We compare the line ratios to the outputs of photodissociation region (PDR) models to constrain the physical conditions in the interstellar medium (ISM) of the SMGs, finding an average density of 〈log (n/cm−3)〉 = 4.3 ± 0.2 and an average radiation field (in terms of the local field value, G0) of 〈log (G0)〉 = 3.9 ± 0.4. Overall, we find the SMGs are most comparable to local ultraluminous infrared galaxies (ULIRGs) in G0 and n; however, a significant tail of 5 of the 14 SMGs are likely best compared to less compact, local starburst galaxies, providing new evidence that many SMGs have extended star formation distributions and are therefore not simply scaled up versions of local ULIRGs. We derive the ISM properties of a sample of quasars also finding that they have higher densities and radiation fields on average than the SMGs, consistent with the more extreme local ULIRGs, and reinforcing their interpretation as transition objects. We explore the limitations of using simple PDR models to understand [C I], which may be concomitant with the bulk H2 mass rather than PDR distributed. We therefore also assess [C I] as a tracer of H2, finding that for our sample SMGs, the H2 masses derived from [C I] are often consistent with those determined from low excitation 12CO. We conclude that [C I] observations provide a useful tool to probe the bulk gas and gas processes occurring within merging SMGs, however more detailed, resolved observations are required to fully exploit [C I] as a diagnostic

Dusty starbursts and the formation of elliptical galaxies: A SCUBA-2 survey of a z = 1.46 cluster

We report the results of a deep SCUBA-2 850 and 450 μm survey for dust-obscured ultra-/luminous infrared galaxies (U/LIRGs) in the field of the z = 1.46 cluster XCS J2215.9−1738. We detect a striking overdensity of submillimeter sources coincident with the core of this cluster: ~3–4 × higher than expected in a blank field. We use the likely radio and mid-infrared counterparts to show that the bulk of these submillimeter sources have spectroscopic or photometric redshifts that place them in the cluster and that their multiwavelength properties are consistent with this association. The average far-infrared luminosities of these galaxies are (1.0 ± 0.1) × 1012 ${L}_{\odot }$, placing them on the U/LIRG boundary. Using the total star formation occurring in the obscured U/LIRG population within the cluster, we show that the resulting mass-normalized star formation rate for this system supports previous claims of a rapid increase in star formation activity in cluster cores out to $z\sim 1.5$, which must be associated with the ongoing formation of the early-type galaxies that reside in massive clusters today

The properties of the interstellar medium within a star-forming galaxy at z= 2.3

We present an analysis of the molecular and atomic gas emission in the rest-frame far-infrared and submillimetre from the lensed z= 2.3 submillimetre galaxy SMM J2135−0102. We obtain very high signal-to-noise ratio detections of 11 transitions from three species and limits on a further 20 transitions from nine species. We use the 12CO, [C i] and HCN line strengths to investigate the gas mass, kinematic structure and interstellar medium (ISM) chemistry and find strong evidence for a two-phase medium within this high-redshift starburst galaxy, comprising a hot, dense, luminous component and an underlying extended cool, low-excitation massive component. Employing a suite of photodissociation region models, we show that on average the molecular gas is exposed to an ultraviolet (UV) radiation field that is ∼1000 times more intense than the Milky Way, with star-forming regions having a characteristic density of n∼ 104 cm−3. Thus, the average ISM density and far-UV radiation field intensity are similar to those found in local ultraluminous infrared galaxies (ULIRGs) and to those found in the central regions of typical starburst galaxies, even though the star formation rate is far higher in this system. The 12CO spectral line energy distribution and line profiles give strong evidence that the system comprises multiple kinematic components with different conditions, including temperature, and line ratios suggestive of high cosmic-ray flux within clouds, likely as a result of high star formation density. We find tentative evidence of a factor of ∼4 temperature range within the system. We expect that such internal structures are common in high-redshift ULIRGs but are missed due to the poor signal-to-noise ratio of typical observations. We show that, when integrated over the galaxy, the gas and star formation surface densities appear to follow the Kennicutt–Schmidt relation, although by comparing our data to high-resolution submillimetre imaging, our data suggest that this relation breaks down on scales of <100 pc. By virtue of the lens amplification, these observations uncover a wealth of information on the star formation and ISM at z∼ 2.3 at a level of detail that has only recently become possible at z < 0.1 and show the potential physical properties that will be studied in unlensed galaxies when the Atacama Large Millimeter Array is in full operation

The LABOCA survey of the Extended Chandra Deep Field-South: clustering of submillimetre galaxies

We present a measurement of the spatial clustering of submillimetre galaxies (SMGs) at z= 1–3. Using data from the 870 μm Large APEX Bolometer Camera (LABOCA) submillimetre survey of the Extended Chandra Deep Field-South, we employ a novel technique to measure the cross-correlation between SMGs and galaxies, accounting for the full probability distributions for photometric redshifts of the galaxies. From the observed projected two-point cross-correlation function we derive the linear bias and characteristic dark matter halo masses for the SMGs. We detect clustering in the cross-correlation between SMGs and galaxies at the >4σ level. Accounting for the clustering of galaxies from their autocorrelation function, we estimate an autocorrelation length for SMGs of Graphic Mpc assuming a power-law slope γ= 1.8, and derive a corresponding dark matter halo mass of Graphic. Based on the evolution of dark matter haloes derived from simulations, we show that that the z= 0 descendants of SMGs are typically massive (∼2–3L*) elliptical galaxies residing in moderate- to high-mass groups (Graphic). From the observed clustering we estimate an SMG lifetime of ∼100 Myr, consistent with lifetimes derived from gas consumption times and star formation time-scales, although with considerable uncertainties. The clustering of SMGs at z∼ 2 is consistent with measurements for optically selected quasi-stellar objects (QSOs), supporting evolutionary scenarios in which powerful starbursts and QSOs occur in the same systems. Given that SMGs reside in haloes of characteristic mass ∼6 × 1012 h−1 M⊙, we demonstrate that the redshift distribution of SMGs can be described remarkably well by the combination of two effects: the cosmological growth of structure and the evolution of the molecular gas fraction in galaxies. We conclude that the powerful starbursts in SMGs likely represent a short-lived but universal phase in massive galaxy evolution, associated with the transition between cold gas-rich, star-forming galaxies and passively evolving systems