116 research outputs found
Difficulties in Mid-Infrared selection of AGN in dwarf galaxies
While 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.Comment: 7 pages, 7 figures, 1 table, accepted for publication on MNRA
Evidence of extended cold molecular gas and dust haloes around z ∼ 2.3 extremely red quasars with ALMA
Large-scale outflows are believed to be an important mechanism in the evolution of galaxies. We can determine the impact of these outflows by studying either current galaxy outflows and their effect in the galaxy or by studying the effect of past outflows on the gas surrounding the galaxy. In this work, we examine the CO(7-6), [C I] (3P1→ 3P0), H2O 211-202, and dust continuum emission of 15 extremely red quasars at z ∼2.3 using ALMA. By investigating the radial surface brightness profiles of both the individual sources and the stacked emission, we detect extended cold gas and dust emission on scales of ∼14 kpc in CO(7-6), [C I](2-1), and dust continuum. This is the first time that the presence of a large amount of molecular gas was detected on large, circumgalactic medium scales around quasar host galaxies using [C i] extended emission. We estimate the dust and molecular gas mass of these haloes to be 107.6 and 1010.6 M⊙, indicating significant dust and molecular gas reservoirs around these extreme quasars. By estimating the time-scale at which this gas can reach these distances by molecular gas outflows (7-32 Myr), we conclude that these haloes are a relic of past AGN or starburst activity, rather than an effect of the current episode of extreme quasar activity
What Drives Galaxy Quenching? Resolving Molecular Gas and Star Formation in the Green Valley
We study quenching in seven green valley galaxies on kpc scales by resolving their molecular gas content using \textsuperscript{12}CO(1-0) observations obtained with NOEMA and ALMA, and their star-formation rate using spatially resolved optical spectroscopy from the MaNGA survey. We perform radial stacking of both datasets to increase the sensitivity to molecular gas and star formation, thereby avoiding biases against strongly quenched regions. We find that both spatially resolved gas fraction () and star formation efficiency () are responsible for quenching green valley galaxies at all radii: both quantities are suppressed with respect to typical star-forming regions. and have roughly equal influence in quenching the outer disc. We are, however, unable to identify the dominant mechanism in the strongly quenched central regions. We find that is reduced by in the central regions, but the star formation rate is too low to be measured, leading to upper limits for the . Moving from the outer disc to central regions, the reduction in is driven by an increasing profile rather than a decreasing profile. The reduced may therefore be caused by a decrease in the gas supply rather than molecular gas ejection mechanisms, such as winds driven by active galactic nuclei. We warn
more generally that studies investigating may be deceiving in inferring the cause of quenching, particularly in the central (bulge-dominated) regions of galaxies.STFC
ER
Detecting the halo heating from AGN feedback with ALMA
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 onto 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 S-Z detection (~3.3) 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
emphasise that detecting an SZ signal is more easily achieved in the visibility
plane than in the (inferred) images. We also confirm a marginal detection
(3.2) 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.Comment: 13 pages, 16 figures. Accepted for publication by MNRA
Quiescent low-mass galaxies observed by JWST in the Epoch of Reionization
The surprising JWST discovery of a quiescent, low-mass () galaxy at redshift (JADES-GS-z7-01-QU) represents a unique
opportunity to study the imprint of feedback processes on early galaxy
evolution. We build a sample of 130 low-mass () galaxies from the SERRA cosmological zoom-in simulations, which show
a feedback-regulated, bursty star formation history (SFH). The fraction of time
spent in an active phase increases with the stellar mass from at to at , and it is in agreement with the value estimated for JADES-GS-z7-01-QU. On average, 30% of the galaxies are
quiescent in the range ; they become the dominant population at
. However, none of these quiescent
systems matches the Spectral Energy Distribution of JADES-GS-z7-01-QU, unless
their SFH is artificially truncated a few Myr after the main star formation
peak. As supernova feedback can only act on a longer timescale (), this implies that the observed abrupt quenching must be caused by a
faster physical mechanism, such as radiation-driven winds.Comment: submitted to ApJ Letters, 5 pages, 4 figure
JWST CEERS & JADES Active Galaxies at z = 4-7 Violate the Local Relation at : Implications for Low-Mass Black Holes and Seeding Models
JWST is revolutionizing our understanding of the high-z Universe by expanding
the black hole horizon, looking farther and to smaller masses, and revealing
the stellar light of their hosts. New detections of high-z systems offer
unprecedented insights into the formation of the first black holes and their
early co-evolution with galaxies. By examining JWST galaxies at z=4-7 that host
H-detected black holes, we investigate (i) the high-z
relation and (ii) the black hole mass distribution,
especially in its low-mass range (). With a
detailed statistical analysis, our findings conclusively reveal a high-z
relation that deviates at confidence level from
the local relation: . Black holes
are overmassive by compared to their local counterparts in
similar galactic hosts. This fact is not due to a selection effect in surveys.
Moreover, our analysis predicts the possibility of detecting in high-z JWST
surveys more black holes with ,
and more with , compared to
local relation's predictions. The lighter black holes preferentially occupy
galaxies with a stellar mass of . We have yet to
detect these sources because (i) they may be inactive (duty cycles 1%-10%),
(ii) the host overshines the AGN, or (iii) the AGN is obscured and not
immediately recognizable by line diagnostics. A search of low-mass black holes
in existing JWST surveys will further test the relation.
Current JWST fields represent a treasure trove of black hole systems at z=4-7;
their detection will provide crucial insights into their early evolution and
co-evolution with their galactic hosts.Comment: Submitted for publication in The Astrophysical Journal Letters. 13
pages, 5 figure
Dwarf satellites of high-z Lyman Break Galaxies: a free lunch for JWST
We show that the James Webb Space Telescope will be able to detect dwarf
satellites of high- Lyman Break Galaxies (LBGs). To this aim, we use
cosmological simulations following the evolution of a typical
LBG up to , and analyse the
observational properties of its five satellite dwarf galaxies (). Modelling their stellar emission and dust
attenuation, we reconstruct their rest-frame UV-optical spectra for .
JWST/NIRCam synthetic images show that the satellites can be spatially resolved
from their host, and their emission is detectable by planned deep surveys.
Moreover, we build synthetic spectral energy distributions and colour-magnitude
diagrams for the satellites. We conclude that the color is a
powerful diagnostic tool for understanding their physical properties once they
have been identified. For example, can be used
to identify star-bursting (), low-mass
() systems, with of their
stars being young and metal-poor ().Comment: 8 pages, 3 figures, accepted for publication in ApJ
Dynamically cold disks in the early Universe: myth or reality?
Theoretical models struggle to reproduce dynamically cold disks with
significant rotation-to-dispersion support() observed in
star-forming galaxies in the early Universe, at redshift . We aim to
explore the possible emergence of dynamically cold disks in cosmological
simulations and to understand if different kinematic tracers can help reconcile
the tension between theory and observations. We use 3218 galaxies from the
SERRA suite of zoom-in simulations, with and
SFR, within range. We generate hyper-spectral
data cubes for 6436 synthetic observations of H and [CII]. We find that
the choice of kinematic tracer strongly influences gas velocity dispersion
estimates. When using H ([CII]) synthetic observations, we observe a
strong (mild) correlation between and . Such a difference arises
mostly for galaxies, for which
for a significant fraction of the sample.
Regardless of the tracer, our predictions suggest the existence of massive
() galaxies with at ,
maintaining cold disks for >10 orbital periods (200Myr). Furthermore, we do not
find any significant redshift dependence for ratio in our
sample. Our simulations predict the existence of dynamically cold disks in the
early Universe. However, different tracers are sensitive to different kinematic
properties. While [CII] effectively traces the thin, gaseous disk of galaxies,
H includes the contribution from ionized gas beyond the disk,
characterized by prevalent vertical or radial motions that may be associated
with outflows. The presence of H halos could be a signature of such
galactic outflows. This emphasizes the importance of combining ALMA and
JWST/NIRspec studies of high-z galaxies.Comment: submitted to A&
Extended and broad Ly α emission around a BAL quasar at z ∼ 5
In 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
∼9×10−19ergs−1cm−2arcsec−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.The research leading to these results has received funding from the European Research Council (ERC) under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement no. 306476. RM acknowledges support from the ERC Advanced Grant 695671 ‘QUENCH’. RM and S. Carniani acknowledge support from the Science and Technology Facilities Council (STFC). S. Cantalupo gratefully acknowledges support from Swiss National Science Foundation grant PP00P2_163824
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