We present the results from a ~ 500 ks Chandra observation of the z = 6.31 QSO SDSS J1030 + 0524. This is the deepest X-ray observation to date of a z ~ 6 QSO. The QSO is detected with a total of 125 ...net counts in the full (0.500A0–7 keV) band and its spectrum can be modeled by a single power-law model with photon index of Γ = 1.81 ± 0.18 and full band flux of f = 3.95 × 10−15 erg s−1 cm−2. When compared with the data obtained by XMM-Newton in 2003, our Chandra observation in 2017 shows a harder (ΔΓ ≈ −0.6) spectrum and a 2.5 times fainter flux. Such a variation, in a timespan of ~ 2 yr rest-frame, is unexpected for such a luminous QSO powered by a > 109M⨀ black hole. The observed source hardening and weakening could be related to an intrinsic variation in the accretion rate. However, the limited photon statistics does not allow us to discriminate between an intrinsic luminosity and spectral change, and an absorption event produced by an intervening gas cloud along the line of sight. We also report the discovery of diffuse X-ray emission that extends for 30″ × 20″ southward of the QSO with a signal-to-noise ratio (S/N) of approximately six, hardness ratio of HR = 0.03+0.20−0.25 HR = 0.03 - 0.25 + 0.20 $\text{HR} = {0.03}_{-0.25}^{+0.20}$ , and soft band flux of f0.5– keV = 1.1+0.3−0.3 × 10−15 erg s−1 cm−2 f 0.5 - 2 keV = 1.1 - 0.3 + 0.3 × 10 - 15 erg s - 1 cm - 2 $ f_{0.5-2\,\text{keV}}={1.1}_{-0.3}^{+0.3}\enspace \times \enspace 1{0}^{-15\enspace }\mathrm{erg}\enspace {\mathrm{s}}^{-1}\;\rm{cm}^{-2}$ , that is not associated to a group or cluster of galaxies. We discuss two possible explanations for the extended emission, which may be either associated with the radio lobe of a nearby, foreground radio galaxy (at z ≈ 1 – 2), or ascribed to the feedback from the QSO itself acting on its surrounding environment, as proposed by simulations of early black hole formation.
Context. The coeval active galactic nuclei (AGN) and galaxy evolution, and the observed local relations between super massive black holes (SMBHs) and galaxy properties suggest some sort of connection ...or feedback between SMBH growth (i.e., AGN activity) and galaxy build-up (i.e., star formation history). Aims. We looked for correlations between average properties of X-ray detected AGN and their far-IR (FIR) detected, star forming host galaxies in order to find quantitative evidence for this connection, which has been highly debated in recent years. Methods. We exploited the rich multiwavelength data set (from X-ray to FIR) available in the COSMOS field for a large sample (692 sources) of AGN and their hosts in the redshift range 0.1 <z< 4. We use X-ray data to select AGN and determine their properties, such as X-ray intrinsic luminosity and nuclear obscuration, and broadband (from UV to FIR) SED fitting results to derive host galaxy properties, such as stellar mass (M∗) and star formation rate (SFR). Results. We find that the AGN 2–10 keV luminosity (LX) and the host 8−1000 μm star formation luminosity (LIRSF) are significantly correlated, even after removing the dependency of both quantities with redshift. However, the average host LIRSF has a flat distribution in bins of AGN LX, while the average AGN LX increases in bins of host LIRSF with logarithmic slope of ~0.7 in the redshift range 0.4 <z< 1.2. We also discuss the comparison between the full distribution of these two quantities and the predictions from hydrodynamical simulations. No other significant correlations between AGN LX and host properties is found. On the other hand, we find that the average column density (NH) shows a clear positive correlation with the host M∗ at all redshifts, but not with the SFR (or LIRSF). This translates into a negative correlation with specific SFR at all redshifts. The same is true if the obscured fraction is computed. Conclusions. Our results are in agreement with the idea, introduced in recent galaxy evolutionary models, that SMBH accretion and SFRs are correlated, but occur with different variability time scales. Finally, the presence of a positive correlation between NH and host M∗ suggests that the column density that we observe in the X-rays is not entirely due to the circumnuclear obscuring torus, but may also include a significant contribution from the host galaxy.
SUPER Kakkad, D.; Mainieri, V.; Vietri, G. ...
Astronomy and astrophysics (Berlin),
10/2020, Letnik:
642
Journal Article
Recenzirano
Odprti dostop
Aims.
The SINFONI survey for Unveiling the Physics and Effect of Radiative feedback (SUPER) aims to trace and characterise ionised gas outflows and their impact on star formation in a statistical ...sample of X-ray selected active galactic nuclei (AGN) at
z
∼ 2. We present the first SINFONI results for a sample of 21 Type 1 AGN spanning a wide range in bolometric luminosity (log
L
bol
= 45.4–47.9 erg s
−1
). The main aims of this paper are to determine the extension of the ionised gas, characterise the occurrence of AGN-driven outflows, and link the properties of such outflows with those of the AGN.
Methods.
We used adaptive optics-assisted SINFONI observations to trace ionised gas in the extended narrow line region using the O
III
λ
5007 line. We classified a target as hosting an outflow if its non-parametric velocity of the O
III
line,
w
80
, was larger than 600 km s
−1
. We studied the presence of extended emission using dedicated point-spread function (PSF) observations, after modelling the PSF from the Balmer lines originating from the broad line region.
Results.
We detect outflows in all the Type 1 AGN sample based on the
w
80
value from the integrated spectrum, which is in the range ∼650–2700 km s
−1
. There is a clear positive correlation between
w
80
and the AGN bolometric luminosity (> 99% correlation probability), and the black hole mass (98% correlation probability). A comparison of the PSF and the O
III
radial profile shows that the O
III
emission is spatially resolved for ∼35% of the Type 1 sample and the outflows show an extension up to ∼6 kpc. The relation between maximum velocity and the bolometric luminosity is consistent with model predictions for shocks from an AGN-driven outflow. The escape fraction of the outflowing gas increases with the AGN luminosity, although for most galaxies, this fraction is less than 10%.
Over the past decade, several works have used the ratio between total (rest 8−1000
μ
m) infrared and radio (rest 1.4 GHz) luminosity in star-forming galaxies (
q
IR
), often referred to as the ...infrared-radio correlation (IRRC), to calibrate the radio emission as a star formation rate (SFR) indicator. Previous studies constrained the evolution of
q
IR
with redshift, finding a mild but significant decline that is yet to be understood. Here, for the first time, we calibrate
q
IR
as a function of
both
stellar mass (
M
⋆
) and redshift, starting from an
M
⋆
-selected sample of > 400 000 star-forming galaxies in the COSMOS field, identified via (
NUV
−
r
)/(
r
−
J
) colours, at redshifts of 0.1 <
z
< 4.5. Within each (
M
⋆
,
z
) bin, we stacked the deepest available infrared/sub-mm and radio images. We fit the stacked IR spectral energy distributions with typical star-forming galaxy and IR-AGN templates. We then carefully removed the radio AGN candidates via a recursive approach. We find that the IRRC evolves primarily with
M
⋆
, with more massive galaxies displaying a systematically lower
q
IR
. A secondary, weaker dependence on redshift is also observed. The best-fit analytical expression is the following:
q
IR
(
M
⋆
,
z
) = (2.646 ± 0.024) × (1 +
z
)
( − 0.023 ± 0.008)
–(0.148 ± 0.013) × (log
M
⋆
/
M
⊙
− 10). Adding the UV dust-uncorrected contribution to the IR as a proxy for the total SFR would further steepen the
q
IR
dependence on
M
⋆
. We interpret the apparent redshift decline reported in previous works as due to low-
M
⋆
galaxies being progressively under-represented at high redshift, as a consequence of binning only in redshift and using either infrared or radio-detected samples. The lower IR/radio ratios seen in more massive galaxies are well described by their higher observed SFR surface densities. Our findings highlight the fact that using radio-synchrotron emission as a proxy for SFR requires novel
M
⋆
-dependent recipes that will enable us to convert detections from future ultra-deep radio surveys into accurate SFR measurements down to low-
M
⋆
galaxies with low SFR.
Context. Determining the average fraction of Lyman continuum (LyC) photons escaping high redshift galaxies is essential for understanding how reionization proceeded in the z> 6 Universe. Aims. We ...want to measure the LyC signal from a sample of sources in the Chandra Deep Field South (CDFS) and COSMOS fields for which ultra-deep VIMOS spectroscopy as well as multi-wavelength Hubble Space Telescope (HST) imaging are available. Methods. We select a sample of 46 galaxies at z ~ 4 from the VIMOS Ultra Deep Survey (VUDS) database, such that the VUDS spectra contain the LyC part, that is, the rest-frame range 880−910 Å. Taking advantage of the HST imaging, we apply a careful cleaning procedure and reject all the sources showing nearby clumps with different colours, that could potentially be lower-redshift interlopers. After this procedure, the sample is reduced to 33 galaxies. We measure the ratio between ionizing flux (LyC at 895 Å) and non-ionizing emission (at ~ 1500 Å) for all individual sources. We also produce a normalized stacked spectrum of all sources. Results. Assuming an intrinsic average Lν(1470) /Lν(895) of 3, we estimate the individual and average relative escape fraction. We do not detect ionizing radiation from any individual source, although we identify a possible LyC emitter with very high Lyα equivalent width (EW). From the stacked spectrum and assuming a mean transmissivity for the sample, we measure a relative escape fraction f escrel = 0.09 ± 0.04. We also look for correlations between the limits in the LyC flux and source properties and find a tentative correlation between LyC flux and the EW of the Lyα emission line. Conclusions. Our results imply that the LyC flux emitted by V = 25−26 star-forming galaxies at z ~ 4 is at most very modest, in agreement with previous upper limits from studies based on broad and narrow band imaging.
ABSTRACT
We present a sample of 151 massive (M* > 1010 M⊙) quiescent galaxies at 2 < z < 5, based on a sophisticated Bayesian spectral energy distribution fitting analysis of the CANDELS UDS and ...GOODS-South fields. Our sample includes a robust sub-sample of 61 objects for which we confidently exclude low-redshift and star-forming solutions. We identify 10 robust objects at z > 3, of which 2 are at z > 4. We report formation redshifts, demonstrating that the oldest objects formed at z > 6; however, individual ages from our photometric data have significant uncertainties, typically ∼0.5 Gyr. We demonstrate that the UVJ colours of the quiescent population evolve with redshift at z > 3, becoming bluer and more similar to post-starburst galaxies at lower redshift. Based upon this, we construct a model for the time evolution of quiescent galaxy UVJ colours, concluding that the oldest objects are consistent with forming the bulk of their stellar mass at z ∼ 6–7 and quenching at z ∼ 5. We report spectroscopic redshifts for two of our objects at z = 3.440 and 3.396, which exhibit extremely weak Ly α emission in ultra-deep VANDELS spectra. We calculate star formation rates based on these line fluxes, finding that these galaxies are consistent with our quiescent selection criteria, provided their Ly α escape fractions are >3 and >10 per cent, respectively. We finally report that our highest redshift robust object exhibits a continuum break at λ ∼ 7000 Å in a spectrum from VUDS, consistent with our photometric redshift of $z_\mathrm{phot}=4.72^{+0.06}_{-0.04}$. If confirmed as quiescent, this object would be the highest redshift known quiescent galaxy. To obtain stronger constraints on the times of the earliest quenching events, high-SNR spectroscopy must be extended to z ≳ 3 quiescent objects.
The ALPINE-ALMA [CII] survey Khusanova, Y.; Bethermin, M.; Le Fèvre, O. ...
Astronomy and astrophysics (Berlin),
05/2021, Letnik:
649
Journal Article
Recenzirano
Odprti dostop
Star formation rate (SFR) measurements at
z
> 4 have relied mostly on the rest-frame far-ultraviolet (FUV) observations. The corrections for dust attenuation based on the IRX-
β
relation are highly ...uncertain and are still debated in the literature. Hence, rest-frame far-infrared (FIR) observations are necessary to constrain the dust-obscured component of the SFR. In this paper, we exploit the rest-frame FIR continuum observations collected by the ALMA Large Program to INvestigate CII at Early times (ALPINE) to directly constrain the obscured SFR in galaxies at 4.4 <
z
< 5.9. We used stacks of continuum images to measure average infrared luminosities taking both detected and undetected sources into account. Based on these measurements, we measured the position of the main sequence of star-forming galaxies and the specific SFR (sSFR) at
z
∼ 4.5 and
z
∼ 5.5. We find that the main sequence and sSFR do not significantly evolve between
z
∼ 4.5 and
z
∼ 5.5, as opposed to lower redshifts. We developed a method to derive the obscured SFR density (SFRD) using the stellar masses or FUV-magnitudes as a proxy of FIR fluxes measured on the stacks and combining them with the galaxy stellar mass functions and FUV luminosity functions from the literature. We obtain consistent results independent of the chosen proxy. We find that the obscured fraction of SFRD is decreasing with increasing redshift, but even at
z
∼ 5.5 it constitutes around 61% of the total SFRD.
ABSTRACT We present the largest high-redshift (3 < z < 6.85) sample of X-ray-selected active galactic nuclei (AGNs) on a contiguous field, using sources detected in the Chandra COSMOS-Legacy survey. ...The sample contains 174 sources, 87 with spectroscopic redshift and the other 87 with photometric redshift (zphot). In this work, we treat zphot as a probability-weighted sum of contributions, adding to our sample the contribution of sources with zphot < 3 but zphot probability distribution >0 at z > 3. We compute the number counts in the observed 0.5-2 keV band, finding a decline in the number of sources at z > 3 and constraining phenomenological models of the X-ray background. We compute the AGN space density at z > 3 in two different luminosity bins. At higher luminosities (logL(2-10 keV) > 44.1 erg s−1), the space density declines exponentially, dropping by a factor of ∼20 from z ∼ 3 to z ∼ 6. The observed decline is ∼80% steeper at lower luminosities (43.55 erg s−1 < logL(2-10 keV) < 44.1 erg s−1) from z ∼ 3 to z ∼ 4.5. We study the space density evolution dividing our sample into optically classified Type 1 and Type 2 AGNs. At logL(2-10 keV) > 44.1 erg s−1, unobscured and obscured objects may have different evolution with redshift, with the obscured component being three times higher at z ∼ 5. Finally, we compare our space density with predictions of quasar activation merger models, whose calibration is based on optically luminous AGNs. These models significantly overpredict the number of expected AGNs at logL (2-10 keV) > 44.1 erg s−1 with respect to our data.
We explore the multiwavelength properties of AGN host galaxies for different classes of radio-selected AGN out to z ≲ 6 via a multiwavelength analysis of about 7700 radio sources in the COSMOS field. ...The sources were selected with the Very Large Array (VLA) at 3 GHz (10 cm) within the VLA–COSMOS 3 GHz Large Project, and cross-matched with multiwavelength ancillary data. This is the largest sample of high-redshift (z ≲ 6) radio sources with exquisite photometric coverage and redshift measurements available. We constructed a sample of moderate-to-high radiative luminosity AGN (HLAGN) via spectral energy distribution decomposition combined with standard X-ray and mid-infrared diagnostics. Within the remainder of the sample we further identified low-to-moderate radiative luminosity AGN (MLAGN) via excess in radio emission relative to the star formation rates in their host galaxies. We show that at each redshift our HLAGN havesystematically higher radiative luminosities than MLAGN and that their AGN power occurs predominantly in radiative form, while MLAGN display a substantial mechanical AGN luminosity component. We found significant differences in the host properties of the two AGN classes, as a function of redshift. At z< 1.5, MLAGN appear to reside in significantly more massive and less star-forming galaxies compared to HLAGN. At z> 1.5, we observed a reversal in the behaviour of the stellar mass distributions with the HLAGN populating the higher stellar mass tail. We interpret this finding as a possible hint of the downsizing of galaxies hosting HLAGN, with the most massive galaxies triggering AGN activity earlier than less massive galaxies, and then fading to MLAGN at lower redshifts. Our conclusion is that HLAGN and MLAGN samples trace two distinct galaxy and AGN populations in a wide range of redshifts, possibly resembling the radio AGN types often referred to as radiative- and jet-mode (or high- and low-excitation), respectively, whose properties might depend on the different availability of cold gas supplies.
We present the VIMOS Ultra Deep Survey (VUDS), a spectroscopic redshift survey of ~10 000 very faint galaxies to study the main phase of galaxy assembly in 2 < z ≃ 6. The survey covers 1 deg2 in ...three separate fields: COSMOS, ECDFS, and VVDS-02h, with the selection of targets based on an inclusive combination of photometric redshifts and colour properties. Spectra covering 3650 < λ < 9350 Å are obtained with VIMOS on the ESO-VLT with integration times of 14h. Here we present the survey strategy, target selection, data processing, and the redshift measurement process with an emphasis on the specific methods used to adapt to this high-redshift range. We discuss the spectra quality and redshift reliability and derive a success rate in redshift measurement of 91%, or 74% by limiting the dataset to the most reliable measurements, down to a limiting magnitude iAB = 25. Measurements are performed all the way down to iAB = 27. The mean redshift of the main sample is z ~ 3 and extends over a broad redshift range mainly in 2 < z < 6. At 3 < z < 5, the galaxies cover a wide range of luminosities −23 < MNUV < −20.5, stellar mass 109M⊙ < M∗ < 1011M⊙, and star formation rates 1M⊙/yr < SFR < 103M⊙/yr. We discuss the spectral properties of galaxies using individual as well asstacked spectra. The comparison between spectroscopic and photometric redshifts as well as colour selection demonstrate the effectiveness of our selection scheme. From about ~ 90% of the data analysed so far, we expect to assemble >6000 galaxies with reliable spectroscopic redshifts in 2 < z < 6 when complete. This makes the VUDS the largest survey at these redshifts and offers the opportunity for unprecedented studies of the star-forming galaxy population and its distribution in large-scale structures during the main phase of galaxy assembly.
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