452 research outputs found
Star Formation Quenching in Quasar Host Galaxies
No full textGalaxy evolution is likely to be shaped by negative feedback from active galactic nuclei (AGN). In the whole range of redshifts and luminosities studied so far, galaxies hosting an AGN frequently show fast and extended outflows consisting in both ionized and molecular gas. Such outflows could potentially quench the start formation within the host galaxy, but a clear evidence of negative feedback in action is still missing. Hereby I will analyse integral-field spectroscopic data for six quasars at z ~ 2.4 obtained with SINFONI in the H- and K-band. All the quasars show [Oiii]λ5007 line detection of fast, extended outflows. Also, the high signal-to-noise SINFONI observations allow the identification of faint narrow Hα emission (FWHM < 500 km/s), which is spatially extended and associated with star formation in the host galaxy. On paper fast outflows are spatially anti-correlated with star-formation powered emission, i.e., star formation is suppressed in the area affected by the outflow. Nonetheless as narrow, spatially-extended Hα emission, indicating star formation rates of at least 50–100 M⊙ yr−1, has been detected, either AGN feedback is not affecting the whole host galaxy, or star formation is completely quenched only by several feedback episodes. On the other hand, a positive feedback scenario, supported by narrow emission in Hα extending along the edges of the outflow cone, suggests that galaxy-wide outflows could also have a twofold role in the evolution of the host galaxy. Finally, I will present CO(3-2) ALMA data for three out of the six QSOs observed with SINFONI. Flux maps obtained for the CO(3-2) transition suggest that molecular gas within the host galaxy is swept away by fast winds. A negative-feedback scenario is supported by the inferred molecular gas mass in all three objects, which is significantly below what observed in non-active main-sequence galaxies at high-z
Difficulties in mid-infrared selection of AGNs in dwarf galaxies
No full textWhile massive black holes (MBHs) are known to inhabit all massive galaxies, their ubiquitous presence in dwarf galaxies has not been confirmed yet, with only a limited number of sources detected so far. Recently, some studies proposed infrared emission as an alternative way to identify MBHs in dwarfs, based on a similar approach usually applied to quasars. In this study, by accurately combining optical and infrared data taking into account resolution effects and source overlapping, we investigate in detail the possible limitations of this approach with current ground-based facilities, finding a quite low (∼0.4 per cent) fraction of active MBH in dwarfs that are luminous in mid-infrared, consistent with several previous results. Our results suggest that the infrared selection is strongly affected by several limitations that make the identification of MBHs in dwarf galaxies currently prohibitive, especially because of the very poor resolution compared to optical surveys, and the likely contamination by nearby sources, although we find a few good candidates worth further follow-ups. Optical, X-ray, and radio observations therefore still represent the most secure way to search for MBH in dwarfs
Gas and star formation from HD and dust emission in a strongly lensed galaxy
No full textABSTRACT
The molecular gas content of high-redshift galaxies is a highly sought-after property. However, H2 is not directly observable in most environments, so its mass is probed through other emission lines (e.g. CO, [C i], [C ii]), or through a gas-to-dust ratio. Each of these methods depends on several assumptions, and are best used in parallel. In this work, we extend an additional molecular gas tracer to high-redshift studies by observing hydrogen deuteride (HD) emission in the strongly lensed z = 5.656 galaxy SPT0346−52 with ALMA. While no HD(1–0) emission is detected, we are able to place an upper limit on the gas mass of . This is used to find a limit on the conversion factor of . In addition, we construct the most complete spectral energy distribution of this source to date, and fit it with a single-temperature modified blackbody using the nested sampling code multinest, yielding a best-fitting dust mass Mdust = 108.92 ± 0.02 M⊙, dust temperature 78.6 ± 0.5 K, dust emissivity spectral index β = 1.81 ± 0.03, and star formation rate SFR = 3800 ± 100 M⊙ yr−1. Using the continuum flux densities to estimate the total gas mass of the source, we find , assuming subsolar metallicity. This implies a CO conversion factor of αCO < 2.2, which is between the standard values for MW-like galaxies and starbursts. These properties confirm that SPT0346−52 is a heavily starbursting, gas-rich galaxy
Extended and broad Lyα emission around a BAL quasar at z ∼ 5
No full textIn this work we report deep MUSE observations of a broad absorption line (BAL) quasar at z ̃ 5, revealing a Ly α nebula with a maximum projected linear size of ̃60 kpc around the quasar (down to our 2σ SB limit per layer of ̃ 9× 10^{-19} erg s^{-1} cm^{-2} arcsec^{-2} for a 1 arcsec2 aperture). After correcting for the cosmological surface brightness dimming, we find that our nebula, at z ̃ 5, has an intrinsically less extended Ly α emission than nebulae at lower redshift. However, such a discrepancy is greatly reduced when referring to comoving distances, which take into account the cosmological growth of dark matter (DM) haloes, suggesting a positive correlation between the size of Ly α nebulae and the sizes of DM haloes/structures around quasars. Differently from the typical nebulae around radio-quiet non-BAL quasars, in the inner regions ( ̃10 kpc) of the circumgalactic medium of our source, the velocity dispersion of the Ly α emission is very high (FWHM > 1000 km s-1), suggesting that in our case we may be probing outflowing material associated with the quasar
Star formation law in the epoch of reionization from [C ii] and C iii] lines
No full textWe present a novel method to simultaneously characterize the star formation law and the interstellar medium properties of galaxies in the epoch of reionization (EoR) through the combination of [C II] 158 μm (and its known relation with star formation rate) and C III] λ1909 Å emission line data. The method, based on a Markov chain Monte Carlo algorithm, allows us to determine the target galaxy average density, n, gas metallicity, Z, and ‘burstiness’ parameter, κs, quantifying deviations from the Kennicutt–Schmidt relation. As an application, we consider COS-3018 (z = 6.854), the only EoR Lyman Break Galaxy so far detected in both [C II] and C III]. We show that COS-3018 is a moderate starburst (κs ≈ 3), with Z ≈ 0.4 Z☉, and n ≈ 500 cm−3. Our method will be optimally applied to joint ALMA and James Webb Space Telescope targets
High [{OIII}]/[{CII}] surface brightness ratios trace early starburst galaxies
No full textWe study the impact of deviations from the Kennicutt–Schmidt relation (quantified by the ‘burstiness’ parameter κs), gas metallicity (Z), and density (n) on the observed [O III]88 μm/[C II]158 μm surface brightness ratios (Σ[O III]/Σ[C II]) in nine galaxies at z ≈ 6−9. We first discuss possible biases in the measured Σ[O III]/Σ[C II] ratios by comparing the data with zoom-in cosmological simulations and then use a Markov Chain Monte Carlo algorithm to derive the best-fitting values of (κs, Z, n). We find that (i) the strongest dependence of Σ[O III]/Σ[C II] is on κs; (ii) high ratios identify starburst galaxies with short gas depletion times (tdep = 6 − 49 Myr); (iii) a secondary dependence on density is found, with Σ[O III]/Σ[C II] anticorrelating with n as a result of the lower [O III] critical density; and (iv) the ratio weakly depends only on Z. The nine galaxies are significantly enriched (Z = 0.2−0.5 Z☉) and dense n ≈ 101−3 cm−3. This lends further support to the starburst scenario in which a rapid enrichment of the interstellar medium is expected
Detecting the halo heating from AGN feedback with ALMA
No full textABSTRACT
The Sunyaev–Zel’dovich (SZ) effect can potentially be used to investigate the heating of the circumgalactic medium and subsequent suppression of cold gas accretion on to the host galaxy caused by quasar feedback. We use a deep ALMA observation of HE0515-4414 in band 4, the most luminous quasar known at the peak of cosmic star formation (z = 1.7), to search for the SZ signal tracing the heating of the galaxy’s halo. ALMA’s sensitivity to a broad range of spatial scales enables us to disentangle emitting compact sources from the negative, extended SZ signal. We obtain a marginal SZ detection (∼3.3σ) on scales of about 300 kpc (30–40 arcsec), at the 0.2 mJy level, 0.5 mJy after applying a correction factor for primary beam attenuation and flux that is resolved out by the array. We show that our result is consistent with a simulated ALMA observation of a similar quasar in the fable cosmological simulations. We emphasize that detecting an SZ signal is more easily achieved in the visibility plane than in the (inferred) images. We also confirm a marginal detection (3.2σ) of a potential SZ dip on smaller scales (<100 kpc) already claimed by other authors, possibly highlighting the complex structure of the halo heating. Finally, we use SZ maps from the fable cosmological simulations, convolved with ALMA simulations, to illustrate that band 3 observations are much more effective in detecting the SZ signal with higher significance, and discuss the optimal observing strategy
ALMA Detection of Extended [C ii] Emission in Himiko at z = 6.6
No full textHimiko is one of the most luminous Lyα emitters at z = 6.595. It has three star-forming clumps detected in the rest-frame UV, with a total SFR = 20 M⊙ yr−1. We report the Atacama Large Millimeter/submillimeter Array (ALMA) detection of the [C ii]158 μm line emission in this Galaxy with a significance of 8σ. The total [C ii] luminosity (L[C ii] = 1.2 × 108 L⊙) is fully consistent with the local L[C ii]–SFR relation. The ALMA high-angular resolution reveals that the [C ii] emission is made of two distinct components. The brightest [C ii] clump is extended over 4 kpc and is located on the peak of the Lyα nebula, which is spatially offset by 1 kpc relative to the brightest UV clump. The second [C ii] component is spatially unresolved (size <2 kpc) and coincident with one of the three UV clumps. While the latter component is consistent with the local L[C ii]–SFR relation, the other components are scattered above and below the local relation. We shortly discuss the possible origin of the [C ii] components and their relation with the star-forming clumps traced by the UV emission
Detection of a high-redshift molecular outflow in a primeval hyperstarburst galaxy
No full textWe report the discovery of a high-redshift, massive molecular outflow in the starburst galaxy SPT0346-52 (z = 5:656) via the detected absorption of high-excitation water transitions (H2O 42;3 41;4 and H2O 33;0 32;1) with the Atacama Large Millimeter/ submillimeter Array (ALMA). The host galaxy is one of the most powerful starburst galaxies at high redshift (star formation rate; SFR ~ 3,600M year{^{-}}1), with an extremely compact (~ 320 pc) star formation region and a star formation rate surface density (SFR ~ 5; 500M year{^{-}}1 kpc{^{-}}2) five times higher than ‘maximum’ (i.e. Eddington-limited) starbursts, implying a highly transient phase. The estimated outflow rate is ~ 500M year{^{-}}1, which is much lower than the SFR, implying that in this extreme starburst the outflow capabilities saturate and the outflow is no longer capable of regulating star formation, resulting in a runaway process in which star formation will use up all available gas in less than 30 Myr. Finally, while previous kinematic investigations of this source revealed possible evidence for an ongoing major merger, the coincidence of the hyper-compact starburst and high-excitation water absorption indicates that this is a single starburst galaxy surrounded by a disc
Widespread QSO-driven outflows in the early Universe⋆
No full textWe present the stacking analysis of a sample of 48 quasi-stellar objects (QSOs) at 4.5 < z < 7.1 detected by the Atacama Large Millimetre Array (ALMA) in the [CII] λ 158 μ m emission line to investigate the presence and the properties of massive, cold outflows associated with broad wings in the [CII] profile. The high sensitivity reached through this analysis allows us to reveal very broad [CII] wings tracing the presence of outflows with velocities in excess of 1000 km s −1 . We find that the luminosity of the broad [CII] emission increases with L AGN , while it does not significantly depend on the star formation rate of the host galaxy, indicating that the central active galactic nucleus (AGN) is the main driving mechanism of the [CII] outflows in these powerful, distant QSOs. From the stack of the ALMA cubes, we derive an average outflow spatial extent of ∼3.5 kpc. The average atomic neutral mass outflow rate inferred from the stack of the whole sample is Ṁ out ∼ 100 M ⊙ yr −1 , while for the most luminous systems it increases to ∼200 M ⊙ yr −1 . The associated outflow kinetic power is about 0.1% of L AGN , while the outflow momentum rate is ∼ L AGN / c or lower, suggesting that these outflows are either driven by radiation pressure onto dusty clouds or, alternatively, are driven by the nuclear wind and energy conserving but with low coupling with the interstellar medium. We discuss the implications of the resulting feedback effect on galaxy evolution in the early Universe
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