The effect of active galactic nuclei on the cold interstellar medium in distant star-forming galaxies

In the framework of a systematic study with the ALMA interferometer of IR-selected main-sequence and starburst galaxies at z ∼ 1 − 1.7 at typical ∼1″ resolution, we report on the effects of mid-IR- and X-ray-detected active galactic nuclei (AGN) on the reservoirs and excitation of molecular gas in a sample of 55 objects. We find widespread detectable nuclear activity in ∼30% of the sample. The presence of dusty tori influences the IR spectral energy distribution of galaxies, as highlighted by the strong correlation among the AGN contribution to the total IR luminosity budget (fAGN = LIR,  AGN/LIR), its hard X-ray emission, and the Rayleigh-Jeans to mid-IR (S1.2 mm/S24 μm) observed color, with evident consequences on the ensuing empirical star formation rate estimates. Nevertheless, we find only marginal effects of the presence and strength of AGN on the carbon monoxide CO (J = 2, 4, 5, 7) or neutral carbon ([C I](3P1  −  3P0), [C I](3P2  −  3P1)) line luminosities and on the derived molecular gas excitation as gauged by line ratios and the full spectral line energy distributions. The [C I] and CO emission up to J = 5, 7 thus primarily traces the properties of the host in typical IR luminous galaxies. However, our analysis highlights the existence of a large variety of line luminosities and ratios despite the homogeneous selection. In particular, we find a sparse group of AGN-dominated sources with the highest LIR,  AGN/LIR,  SFR ratios, ≳3, that are more luminous in CO (5−4) than what is predicted by the L′CO(5-4)−LIR, SFR relation, which might be the result of the nuclear activity. For the general population, our findings translate into AGN having minimal effects on quantities such as gas and dust fractions and star formation efficiencies. If anything, we find hints of a marginal tendency of AGN hosts to be compact at far-IR wavelengths and to display 1.8 times larger dust optical depths. In general, this is consistent with a marginal impact of the nuclear activity on the gas reservoirs and star formation in average star-forming AGN hosts with LIR > 5 × 1011 L⊙, typically underrepresented in surveys of quasars and submillimeter galaxies

CO emission in distant galaxies on and above the main sequence

We present the detection of multiple carbon monoxide CO line transitions with ALMA in a few tens of infrared-selected galaxies on and above the main sequence at z = 1.1−1.7. We reliably detected the emission of CO (5−4), CO (2−1), and CO (7−6)+[C I](3P2 − 3P1) in 50, 33, and 13 galaxies, respectively, and we complemented this information with available CO (4 − 3) and [C I](3P1 − 3P0) fluxes for part of the sample, and by modeling of the optical-to-millimeter spectral energy distribution. We retrieve a quasi-linear relation between LIR and CO (5 − 4) or CO (7 − 6) for main-sequence galaxies and starbursts, corroborating the hypothesis that these transitions can be used as star formation rate (SFR) tracers. We find the CO excitation to steadily increase as a function of the star formation efficiency, the mean intensity of the radiation field warming the dust (hUi), the surface density of SFR (ΣSFR), and, less distinctly, with the distance from the main sequence (∆MS). This adds to the tentative evidence for higher excitation of the CO+[C I] spectral line energy distribution (SLED) of starburst galaxies relative to that for main-sequence objects, where the dust opacities play a minor role in shaping the high-J CO transitions in our sample. However, the distinction between the average SLED of upper main-sequence and starburst galaxies is blurred, driven by a wide variety of intrinsic shapes. Large velocity gradient radiative transfer modeling demonstrates the existence of a highly excited component that elevates the CO SLED of high-redshift main-sequence and starbursting galaxies above the typical values observed in the disk of the Milky Way. This excited component is dense and it encloses ∼50% of the total molecular gas mass in main-sequence objects. We interpret the observed trends involving the CO excitation as to be mainly determined by a combination of large SFRs and compact sizes, as a large ΣSFR is naturally connected with enhanced dense molecular gas fractions and higher dust and gas temperatures, due to increasing ultraviolet radiation fields, cosmic ray rates, as well as dust and gas coupling. We release the full data compilation and the ancillary information to the community

Close-up view of a luminous star-forming galaxy at <i>z</i> = 2.95*

Exploiting the sensitivity of the IRAM NOrthern Extended Millimeter Array (NOEMA) and its ability to process large instantaneous bandwidths, we have studied the morphology and other properties of the molecular gas and dust in the star forming galaxy, H-ATLAS J131611.5+281219 (HerBS-89a), at z = 2.95. High angular resolution (0.″3) images reveal a partial 1.″0 diameter Einstein ring in the dust continuum emission and the molecular emission lines of 12CO(9−8) and H2O(202 − 111). Together with lower angular resolution (0.″6) images, we report the detection of a series of molecular lines including the three fundamental transitions of the molecular ion OH+, namely (11 − 01), (12 − 01), and (10 − 01), seen in absorption; the molecular ion CH+(1 − 0) seen in absorption, and tentatively in emission; two transitions of amidogen (NH2), namely (202 − 111) and (220 − 211) seen in emission; and HCN(11 − 10) and/or NH(12 − 01) seen in absorption. The NOEMA data are complemented with Very Large Array data tracing the 12CO(1 − 0) emission line, which provides a measurement of the total mass of molecular gas and an anchor for a CO excitation analysis. In addition, we present Hubble Space Telescope imaging that reveals the foreground lensing galaxy in the near-infrared (1.15 μm). Together with photometric data from the Gran Telescopio Canarias, we derive a photometric redshift of zphot = 0.9−0.5+0.3 for the foreground lensing galaxy. Modeling the lensing of HerBS-89a, we reconstruct the dust continuum (magnified by a factor μ ≃ 5.0) and molecular emission lines (magnified by μ ∼ 4 − 5) in the source plane, which probe scales of ∼0.″1 (or 800 pc). The 12CO(9 − 8) and H2O(202 − 111) emission lines have comparable spatial and kinematic distributions; the source-plane reconstructions do not clearly distinguish between a one-component and a two-component scenario, but the latter, which reveals two compact rotating components with sizes of ≈1 kpc that are likely merging, more naturally accounts for the broad line widths observed in HerBS-89a. In the core of HerBS-89a, very dense gas with nH2 ∼ 107 − 9 cm−3 is revealed by the NH2 emission lines and the possible HCN(11 − 10) absorption line. HerBS-89a is a powerful star forming galaxy with a molecular gas mass of Mmol = (2.1 ± 0.4) × 1011 M⊙, an infrared luminosity of LIR = (4.6 ± 0.4) × 1012 L⊙, and a dust mass of Mdust = (2.6 ± 0.2) × 109 M⊙, yielding a dust-to-gas ratio δGDR ≈ 80. We derive a star formation rate SFR = 614 ± 59 M⊙ yr−1 and a depletion timescale τdepl = (3.4 ± 1.0) × 108 years. The OH+ and CH+ absorption lines, which trace low (∼100 cm−3) density molecular gas, all have their main velocity component red-shifted by ΔV ∼ 100 km s−1 relative to the global CO reservoir. We argue that these absorption lines trace a rare example of gas inflow toward the center of a galaxy, indicating that HerBS-89a is accreting gas from its surroundings

Extinction in the 11.2 μm PAH band and the low L11.2/LIRin ULIRGs

We present a method for recovering the intrinsic (extinction-corrected) luminosity of the 11.2 μm PAH band in galaxy spectra. Using 105 high S/N Spitzer/IRS spectra of star-forming galaxies, we show that the equivalent width ratio of the 12.7 and 11.2 μm PAH bands is independent on the optical depth (t), with small dispersion (5 per cent) indicative of a nearly constant intrinsic flux ratio Rint = (f12.7/f11.2)int = 0.377 ± 0.020. Conversely, the observed flux ratio, Robs = (f12.7/f11.2)obs, strongly correlates with the silicate strength (Ssil) confirming that differences in Robs reflect variation in t . The relation between Robs and Ssil reproduces predictions for the Galactic Centre extinction law but disagrees with other laws.We calibrate the total extinction affecting the 11.2 μmPAHfrom Robs,which we apply to another sample of 215 galaxies with accuratemeasurements of the total infrared luminosity (LIR) to investigate the impact of extinction on L11.2/LIR. Correlation between L11.2/LIR and Robs independently on LIR suggests that increased extinction explains the well-known decrease in the average L11.2/LIR at high LIR. The extinction-corrected L11.2 is proportional to LIR in the range LIR = 109-1013 L⊙. These results consolidate L11.2 as a robust tracer of star formation in galaxies.With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737

PAHs as tracers of the molecular gas in star-forming galaxies

International audienc

The evolving interstellar medium of star-forming galaxies, as traced by Stardust

International audienceWe analyze the far-infrared (FIR) properties of \raisebox-0.5ex~5000 star-forming galaxies at z < 4.5, drawn from the deepest, super-deblended catalogs in the GOODS-N and COSMOS fields. We develop a novel panchromatic spectral energy distribution fitting algorithm, Stardust, that models the emission from stars, active galactic nuclei (AGNs), and infrared dust emission, without relying on energy balance assumptions. Our code provides robust estimates of the UV- optical and FIR physical parameters, such as the stellar mass ($M_*$), dust mass ($M_{dust}$), infrared luminosities (L$_{IR}$) arising from AGN and star formation activity, and the average intensity of the interstellar radiation field (⟨U⟩). Through a set of simulations we quantify the completeness of our data in terms of $M_{_dust}$, $L_{IR}$, and ⟨U⟩ and subsequently characterize the distribution and evolution of these parameters with redshift. We focus on the dust-to-stellar mass ratio ($f_{dust}$), which we parameterize as a function of cosmic age, stellar mass, and specific star formation rate. The $f_{dust}$) is found to increase by a factor of 10 from z = 0 to z = 2 and appears to remain flat at higher z, mirroring the evolution of the gas fraction. We also find a growing fraction of warm to cold dust with increasing distance from the main sequence, indicative of more intense interstellar radiation fields, higher star formation efficiencies, and more compact star-forming regions for starburst galaxies. Finally, we construct the dust mass functions (DMFs) of star-forming galaxies up to z = 1 by transforming the stellar mass function to DMF through the scaling relations derived here. The evolution of $f_{dust}$) and the recovered DMFs are in good agreement with the theoretical predictions of the Horizon-AGN and IllustrisTNG simulations

Starburst to Quiescent from HST/ALMA: Stars and Dust Unveil Minor Mergers in Submillimeter Galaxies at z ∼ 4.5

Dust-enshrouded, starbursting, submillimeter galaxies (SMGs) at z ≥ 3 have been proposed as progenitors of z ≥ 2 compact quiescent galaxies (cQGs). To test this connection, we present a detailed spatially resolved study of the stars, dust, and stellar mass in a sample of six submillimeter-bright starburst galaxies at z ∼ 4.5. The stellar UV emission probed by HST is extended and irregular and shows evidence of multiple components. Informed by HST, we deblend Spitzer/IRAC data at rest-frame optical, finding that the systems are undergoing minor mergers with a typical stellar mass ratio of 1:6.5. The FIR dust continuum emission traced by ALMA locates the bulk of star formation in extremely compact regions (median r = 0.70 ± 0.29 kpc), and it is in all cases associated with the most massive component of the mergers (median ). We compare spatially resolved UV slope (β) maps with the FIR dust continuum to study the infrared excess (IRX = L /L )-β relation. The SMGs display systematically higher IRX values than expected from the nominal trend, demonstrating that the FIR and UV emissions are spatially disconnected. Finally, we show that the SMGs fall on the mass-size plane at smaller stellar masses and sizes than the cQGs at z = 2. Taking into account the expected evolution in stellar mass and size between z = 4.5 and z = 2 due to the ongoing starburst and mergers with minor companions, this is in agreement with a direct evolutionary connection between the two populations. © 2018. The American Astronomical Society. All rights reserved..C.G.G. and S.T. acknowledge support from the European Research Council (ERC) Consolidator Grant funding scheme (project ConTExt, grant number 648179). A.K., E.J.A., and F.B. acknowledge support by the Collaborative Research Centre 956, subproject A1, funded by the Deutsche Forschungsgemeinschaft (DFG). Support for B.M. was provided by the DFG priority program 1573, "The physics of the interstellar medium." D.R. acknowledges support from the National Science Foundation under grant number AST-1614213. V.S. acknowledges support from the European Union's Seventh Framework program under grant agreement 337595 (ERC Starting Grant, "CoSMass"). M.A. acknowledges partial support from FONDECYT through grant 1140099. ERD also acknowledge support by the Collaborative Research Centre 956, subproject C4, funded by the DFG. M.J.M. acknowledges the support of the National Science Centre, Poland, through POLONEZ grant 2015/19/P/ST9/04010; this project has received funding from the European Union's Horizon 2020 research and innovation program under Marie Sklodowska-Curie grant agreement No. 665778. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #13294. Support for program #13294 was provided by NASA through a grant from the Space Telescope Science Institute

Starburst to Quiescent from HST/ALMA: Stars and Dust Unveil Minor Mergers in Submillimeter Galaxies at z ̃ 4.5

Dust-enshrouded, starbursting, submillimeter galaxies (SMGs) at z ≥ 3 have been proposed as progenitors of z ≥ 2 compact quiescent galaxies (cQGs). To test this connection, we present a detailed spatially resolved study of the stars, dust, and stellar mass in a sample of six submillimeter-bright starburst galaxies at z ̃ 4.5. The stellar UV emission probed by HST is extended and irregular and shows evidence of multiple components. Informed by HST, we deblend Spitzer/IRAC data at rest-frame optical, finding that the systems are undergoing minor mergers with a typical stellar mass ratio of 1:6.5. The FIR dust continuum emission traced by ALMA locates the bulk of star formation in extremely compact regions (median r e = 0.70 ± 0.29 kpc), and it is in all cases associated with the most massive component of the mergers (median {log}({M}* /{M}☉ )=10.49+/- 0.32). We compare spatially resolved UV slope (β) maps with the FIR dust continuum to study the infrared excess (IRX = L IR/L UV)-β relation. The SMGs display systematically higher IRX values than expected from the nominal trend, demonstrating that the FIR and UV emissions are spatially disconnected. Finally, we show that the SMGs fall on the mass-size plane at smaller stellar masses and sizes than the cQGs at z = 2. Taking into account the expected evolution in stellar mass and size between z = 4.5 and z = 2 due to the ongoing starburst and mergers with minor companions, this is in agreement with a direct evolutionary connection between the two populations

Globalfocusing: from domestic conglomerates to global specialists

Globalization is changing the competitive terrain on which companies develop their corporate strategy. On the global stage, key competitive advantages are gained through internationally fungible resources. Consequently, diversified conglomerates are converting to global specialists in narrower niche markets and competing with a small number of multinational enterprises operating worldwide. Their "internationalization" and their reduction of product "diversification" are opposite sides of the same coin: "globalfocusing". I extend Penrosian resource-based theory to analyse this change process, notably by distinguishing country and industry specificity of firms' core competences, and by integrating divestment as part of firm growth processes. Globalfocusing is driven by shifts in the relative importance of country-specific and industry-specific resources and capabilities due to changes in the internal and external environment, notably the globalization of markets and supply chains. The argument is developed using case studies of restructuring of two Danish manufacturing enterprises. On this basis, I analyse the forces driving globalfocusing processes and suggest propositions for empirical testing. Copyright Blackwell Publishing Ltd 2006.