54 research outputs found
Experimental Indicators of Accretion Processes in Active Galactic Nuclei
Bright Active Galactic Nuclei are powered by accretion of mass onto the super
massive black holes at the centers of the host galaxies. For fainter objects
star formation may significantly contribute to the luminosity. We summarize
experimental indicators of the accretion processes in Active Galactic Nuclei
(AGN), i.e., observable activity indicators that allow us to conclude on the
nature of accretion. The Galactic Center is the closest galactic nucleus that
can be studied with unprecedented angular resolution and sensitivity.
Therefore, here we also include the presentation of recent observational
results on Sagittarius A* and the conditions for star formation in the central
stellar cluster. We cover results across the electromagnetic spectrum and find
that the Sagittarius A* (SgrA*) system is well ordered with respect to its
geometrical orientation and its emission processes of which we assume to
reflect the accretion process onto the super massive black hole.Comment: 16 pages, 4 figures, conference proceeding: Accretion Processes in
Cosmic Sources - APCS2016 - 5-10 September 2016, Saint Petersburg, Russi
Monitoring the Dusty S-Cluster Object (DSO/G2) on its Orbit towards the Galactic Center Black Hole
We analyse and report in detail new near-infrared (1.45 - 2.45 microns)
observations of the Dusty S-cluster Object (DSO/G2) during its approach to the
black hole at the center of the Galaxy that were carried out with ESO
VLT/SINFONI between February and September 2014. Before May 2014 we detect
spatially compact Br-gamma and Pa-alpha line emission from the DSO at about
40mas east of SgrA*. The velocity of the source, measured from the red-shifted
emission, is 2700+-60 km/s. No blue-shifted emission above the noise level is
detected at the position of SgrA* or upstream the presumed orbit. After May we
find spatially compact Br-gamma blue-shifted line emission from the DSO at
about 30mas west of SgrA* at a velocity of -3320+-60 km/s and no indication for
significant red-shifted emission. We do not detect any significant extension of
velocity gradient across the source. We find a Br-gamma-line full width at half
maximum of 50+-10 Angstroem before and 15+-10 Angstroem after the peribothron
transit, i.e. no significant line broadening with respect to last year is
observed. Br-gamma line maps show that the bulk of the line emission originates
from a region of less than 20mas diameter. This is consistent with a very
compact source on an elliptical orbit with a peribothron time passage in
2014.39+-0.14. For the moment, the flaring activity of the black hole in the
near-infrared regime has not shown any statistically significant increment.
Increased accretion activity of SgrA* may still be upcoming. We discuss details
of a source model according to which the DSO is rather a young accreting star
than a coreless gas and dust cloud.Comment: 32 pages - 3 tables - 17 figure - accepted by Ap
Uncovering the stellar structure of the dusty star-forming galaxy GN20 at z=4.055 with MIRI/JWST
Luminous infrared galaxies at high redshifts (>4) include extreme
starbursts that build their stellar mass over short periods of time (>100 Myr).
These galaxies are considered to be the progenitors of massive quiescent
galaxies at intermediate redshifts (2) but their stellar structure and
buildup is unknown. Here, we present the first spatially resolved near-infrared
imaging of GN20, one of the most luminous dusty star-forming galaxies known to
date, observed at an epoch when the Universe was only 1.5 Gyr old. The
5.6m image taken with the JWST Mid-Infrared Instrument (MIRI/JWST) shows
that GN20 is a very luminous galaxy (M=25.01), with a
stellar structure composed of a conspicuous central source and an extended
envelope. The central source is an unresolved nucleus that carries 9% of the
total flux. The nucleus is co-aligned with the peak of the cold dust emission,
and offset by 3.9 kpc from the ultraviolet stellar emission. The diffuse
stellar envelope is similar in size to the clumpy CO molecular gas
distribution. The centroid of the stellar envelope is offset by 1 kpc from the
unresolved nucleus, suggesting GN20 is involved in an interaction or merger
event supported by its location as the brightest galaxy in a proto-cluster. The
stellar size of GN20 is larger by a factor of about 3-5 than known spheroids,
disks, and irregulars at 4, while its size and low S\'ersic index are
similar to those measured in dusty, infrared luminous galaxies at 2 of
the same mass. GN20 has all the ingredients necessary for evolving into a
massive spheroidal quiescent galaxy at intermediate : it is a large,
luminous galaxy at =4.05 involved in a short and massive starburst centred
in the stellar nucleus and extended over the entire galaxy, out to radii of 4
kpc, and likely induced by the interaction or merger with a member of the
proto-cluster.Comment: 7 pages, 4 figure
MIDIS. JWST NIRCam and MIRI unveil the stellar population properties of Ly-emitters and Lyman-Break galaxies at z ~ 3-7
We study the stellar population properties of 182 spectroscopically-confirmed
(MUSE/VLT) Lyman- emitters (LAEs) and 450 photometrically-selected
Lyman-Break galaxies (LBGs) at z = 2.8 - 6.7 in the Hubble eXtreme Deep Field
(XDF). Leveraging the combined power of HST and JWST NIRCam and MIRI
observations, we analyse their rest-frame UV-through-near-IR spectral energy
distributions (SEDs) with MIRI playing a crucial role in robustly assessing the
LAE's stellar mass and ages. Our LAEs are low-mass objects
(log(M[M]) ~ 7.5), with little or no dust extinction
(E(B - V) ~ 0.1) and a blue UV continuum slope ( ~ -2.2). While 75% of
our LAEs are young (< 100 Myr), the remaining 25% have significantly older
stellar populations (> 100 Myr). These old LAEs are statistically more massive,
less extinct and have lower specific star formation rate (sSFR) compared to
young LAEs. Besides, they populate the M - SFR plane along the
main-sequence (MS) of star-forming galaxies, while young LAEs populate the
starburst region. The comparison between the LAEs properties to those of a
stellar-mass matched sample of LBGs shows no statistical difference between
these objects, except for the LBGs redder UV continuum slope and marginally
larger E(B - V) values. Interestingly, 48% of the LBGs have ages < 10 Myr and
are classified as starbursts, but lack detectable Ly emission. This is
likely due to HI resonant scattering and/or selective dust extinction. Overall,
we find that JWST observations are crucial in determining the properties of
LAEs and shedding light on the properties and similarities between LAEs and
LBGs.Comment: 19 pages, 15 figures, 5 tables. Submitted to AP
Strong (Hb + [OIII]) and Ha emitters at redshift z ~ 7-8 unveiled with JWST/NIRCam and MIRI imaging in the Hubble eXtreme Deep Field (XDF)
The JWST is revolutionizing the study of high-redshift galaxies by providing
for the first time a high-sensitivity view of the early Universe at infrared
wavelengths, both with its Near Infrared Camera (NIRCam) and Mid Infrared
Instrument (MIRI). In this paper, we make use of medium and broad-band NIRCam
imaging, as well as ultra-deep MIRI 5.6 microns imaging, in the Hubble eXtreme
Deep Field (XDF) to identify prominent line emitters at z ~ 7-8. Out of a total
of 58 galaxies at z ~ 7-8, we find 18 robust candidates (~31%) for prominent
(Hb + [OIII]) emitters, based on their enhanced fluxes in the F430M and F444W
filters, with rest-frame EW(Hb + [OIII]) ~ 87 - 2100 A. Among these emitters,
16 lie on the MIRI coverage area and 12 show a clear flux excess at 5.6
microns, indicating the simultaneous presence of a prominent Ha emission line
with rest-frame EW(Ha) ~ 200 - 3000 A. This is the first time that Ha emission
can be detected in individual galaxies at z>7. The Ha line, when present,
allows us to separate the contributions of the Hb and [OIII] emission lines to
the (Hb + [OIII]) complex and derive Ha-based star formation rates (SFRs). We
find that in some cases [OIII]/Hb > 1, suggesting low metallicities, but a few
have [OIII]/Hb < 1, so the NIRCam flux excess is mainly driven by Hb. The vast
majority of prominent line emitters are very young starbursts or galaxies on
their way to/from the starburst cloud. They make for a cosmic SFR density
log10(SFRD_Ha / Msun yr^-1 Mpc^-3) ~ 2.35, which is about a third of the total
value at z ~ 7-8. Therefore, the strong Ha emitters likely had an important
role in reionization.Comment: 15 pages, 9 figures. Submitted to Ap
Life beyond 30: Probing the â20 < M UV < â17 Luminosity Function at 8 < z < 13 with the NIRCam Parallel Field of the MIRI Deep Survey
We present the ultraviolet luminosity function and an estimate of the cosmic star formation rate density at 8 8 galaxy candidates based on their dropout nature in the F115W and/or F150W filters, a high probability for their photometric redshifts, estimated with three different codes, being at z > 8, good fits based on Ï2 calculations, and predominant solutions compared to z < 8 alternatives. We find mild evolution in the luminosity function from z ⌠13 to z ⌠8, i.e., only a small increase in the average number density of âŒ0.2 dex, while the faint-end slope and absolute magnitude of the knee remain approximately constant, with values α = â 2.2 ± 0.1, and M* = â 20.8 ± 0.2 mag. Comparing our results with the predictions of state-of-the-art galaxy evolution models, we find two main results: (1) a slower increase with time in the cosmic star formation rate density compared to a steeper rise predicted by models; (2) nearly a factor of 10 higher star formation activity concentrated in scales around 2 kpc in galaxies with stellar masses âŒ108Mâ during the first 350 Myr of the universe, z ⌠12, with models matching better the luminosity density observational estimations âŒ150 Myr later, by z ⌠9
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