32 research outputs found
Hypercompact stellar clusters: morphological renditions and spectro-photometric models
Numerical relativity predicts that the coalescence of a black hole-binary
causes the newly formed black hole to recoil, and evidence for such recoils has
been found in the gravitational waves observed during the merger of
stellar-mass black holes. Recoiling (super)massive black holes are expected to
reside in hypercompact stellar clusters (HCSCs). Simulations of galaxy assembly
predict that hundreds of HCSCs should be present in the halo of a Milky
Way-type galaxy, and a fraction of those around the Milky Way should have
magnitudes within the sensitivity limit of existing surveys. However, recoiling
black holes and their HCSCs are still waiting to be securely identified. With
the goal of enabling searches through recent and forthcoming databases, we
improve over existing literature to produce realistic renditions of HCSCs bound
to black holes with a mass of 10 M. Including the effects of a
population of blue stragglers, we simulate their appearance in Pan-STARRS and
in forthcoming images. We also derive broad-band spectra and the
corresponding multi-wavelength colours, finding that the great majority of the
simulated HCSCs fall on the colour-colour loci defined by stars and galaxies,
with their spectra resembling those of giant K-type stars. We discuss the
clusters properties, search strategies, and possible interlopers.Comment: Accepted for publication on MNRAS, 17 pages, 7 figure
Chemical abundances of two extragalactic young massive clusters
Aims. We use integrated-light spectroscopic observations to measure metallicities and chemical abundances for two extragalactic young massive star clusters (NGCâ1313-379 and NGCâ1705-1). The spectra were obtained with the X-shooter spectrograph on the ESO Very Large Telescope.
Methods. We compute synthetic integrated-light spectra, based on colour-magnitude diagrams (CMDs) for the brightest stars in the clusters from Hubble Space Telescope photometry and theoretical isochrones. Furthermore, we test the uncertainties arising from the use of CMD+Isochrone method compared to an Isochrone-Only method. The abundances of the model spectra are iteratively adjusted until the best fit to the observations is obtained. In this work we mainly focus on the optical part of the spectra.
Results. We find metallicities of [Fe/H] = â0.84 ± 0.07 and [Fe/H] = â0.78 ± 0.10 for NGCâ1313-379 and NGCâ1705-1, respectively. We measure [α/Fe]â=â+0.06 ± 0.11 for NGCâ1313-379 and a super-solar [α/Fe]â=â+0.32 ± 0.12 for NGCâ1705-1. The roughly solar [α/Fe] ratio in NGCâ1313-379 resembles those for young stellar populations in the Milky Way (MW) and the Magellanic Clouds, whereas the enhanced [α/Fe] ratio in NGCâ1705-1 is similar to that found for the cluster NGCâ1569-B by previous studies. Such super-solar [α/Fe] ratios are also predicted by chemical evolution models that incorporate the bursty star formation histories of these dwarf galaxies. Furthermore, our α-element abundances agree with abundance measurements from H II regions in both galaxies. In general we derive Fe-peak abundances similar to those observed in the MW and Large Magellanic Cloud (LMC) for both young massive clusters. For these elements, however, we recommend higher-resolution observations to improve the Fe-peak abundance measurements
MAPPING THE NUCLEAR OUTFLOW OF THE MILKY WAY: STUDYING THE KINEMATICS AND SPATIAL EXTENT OF THE NORTHERN FERMI BUBBLE
We report new observations from a systematic, spectroscopic, ultraviolet
absorption-line survey that maps the spatial and kinematic properties of the
high-velocity gas in the Galactic Center region. We examine the hypothesis that
this gas traces the biconical nuclear outflow. We use ultraviolet spectra of 47
background QSOs and halo stars projected inside and outside the northern Fermi
Bubble from the Hubble Space Telescope to study the incidence of high velocity
absorption around it. We use five lines of sight inside the northern Fermi
Bubble to constrain the velocity and column densities of outflowing gas traced
by O I, Al II, C II, C IV, Si II, Si III, Si IV and other species. All five
lines of sight inside the northern Fermi Bubble exhibit blueshifted high
velocity absorption components, whereas only 9 out of the 42 lines of sight
outside the northern Fermi Bubble exhibit blueshifted high velocity absorption
components. The observed outflow velocity profile decreases with Galactic
latitude and radial distance (R) from the Galactic Center. The observed
blueshifted velocities change from =-265 km/s at R~2.3 kpc to
=-91 km/s at R~6.5 kpc. We derive the metallicity of the entrained gas
along the 1H1613-097 sightline, which passes through the center of the northern
Fermi Bubble, finding [O/H] . A simple kinematic model
tuned to match the observed absorption component velocities along the five
lines of sight inside the Bubble, constrains the outflow velocities to
~10001300 km/s, and the age of the outflow to be ~ 69 Myr. We estimate a
minimum mass outflow rate for the nuclear outflow to be 0.2 . Combining the age and mass outflow rates, we determine a
minimum mass of total UV absorbing cool gas entrained in the Fermi Bubbles to
be .Comment: 24 pages, 9 9 figures, Accepted for Publication in Ap
Dissecting the Mid-Infrared Heart of M83 with JWST
We present a first look at the MRS observations of the nucleus of the spiral
galaxy M83, taken with MIRI onboard JWST. The observations show a rich set of
emission features from the ionized and warm molecular gas, as well as traces of
the dust properties in this highly star forming environment. To begin
dissecting the complex processes taking place in this part of the galaxy, we
divide the nucleus observations into four different regions. We find that the
strength of the emission features appears to strongly vary in all four regions,
with the south-east region displaying the weakest features tracing both the
dust continuum and ISM properties. Comparison between the cold molecular gas
traced by the CO (1-0) transition with ALMA and the H 0-0 S(1)
transition showed a similar spatial distribution throughout the nucleus. This
is in contrast to the distribution of the much warmer H emission from the
S(7) transition found to be concentrated mainly around the optical nucleus. We
modeled the H excitation using the rotational emission lines and estimate a
total molecular gas mass accounting for the warm H component of M(50
K) = 59.33 () 10 M. We
compared this value to the total molecular gas mass inferred by probing the
cold H gas through the CO (1-0) emission, M(CO) =
14.99 10 M. Our findings indicate that 75\% of
the total molecular gas mass in the core of M83 is contained in the warm H
component. We also identify [OIV]25.89 m and [FeII]25.99 m emission
(indicative of shocks) in all four nuclear regions with the strongest emission
originating from the north-west section. We propose that the diffuse
[FeII]25.99 m emission is an indication of the combined effects of both
the collective supernova explosions and the starbursts themselves.Comment: 13 pages, 3 Tables, 8 Figures, to be submitted to Ap
CLusters in the Uv as EngineS (CLUES). II. Sub-kpc scale outflows driven by stellar feedback
We analyze the far-ultraviolet spectroscopy of 20 young and massive star
clusters (YSCs) in 11 nearby star-forming galaxies. We probe the interstellar
gas intervening along the line of sight, detecting several metal absorption
lines of a wide range of ionization potentials, from 6.0 eV to 77.5 eV.
Multiple-component Voigt fits to the absorption lines are used to study the
kinematics of the gas. We find that nearly all targets in the sample feature
gas outflowing from 30 up to 190 km per second, often both in the neutral and
ionized phase. The outflow velocities correlate with the underlying stellar
population properties directly linked to the feedback: the mass of the YSCs,
the photon production rate and the instantaneous mechanical luminosity produced
by stellar winds and SNe. We detect a neutral inflow in 4 targets, which we
interpret as likely not associated with the star cluster but tracing larger
scale gas kinematics. A comparison between the outflows energy and that
produced by the associated young stellar populations suggests an average
coupling efficiency of 10 per cent with a broad scatter. Our results extend the
relation found in previous works between galactic outflows and the host galaxy
star-formation rate to smaller scales, pointing towards the key role that
clustered star formation and feedback play in regulating galaxy growth.Comment: Accepted for publication on the Astronomical Journal on 14th February
2024. 32 pages, 13 figure
CLASSY VIII: Exploring the Source of Ionization with UV ISM diagnostics in local High- Analogs
In the current JWST era, rest-frame UV spectra play a crucial role in
enhancing our understanding of the interstellar medium (ISM) and stellar
properties of the first galaxies in the epoch of reionization (EoR, ).
Here, we compare well-known and reliable optical diagrams sensitive to the main
ionization source (i.e., star formation, SF; active galactic nuclei, AGN;
shocks) to UV counterparts proposed in the literature - the so-called ``UV-BPT
diagrams'' - using the HST COS Legacy Archive Spectroscopic SurveY (CLASSY),
the largest high-quality, high-resolution and broad-wavelength range atlas of
far-UV spectra for 45 local star-forming galaxies. In particular, we explore
where CLASSY UV line ratios are located in the different UV diagnostic plots,
taking into account state-of-the-art photoionization and shock models and, for
the first time, the measured ISM and stellar properties (e.g., gas-phase
metallicity, ionization parameter, carbon abundance, stellar age). We find that
the combination of C III] 1907,9 He II and O III]
1666 can be a powerful tool to separate between SF, shocks and AGN at
sub-solar metallicities. We also confirm that alternative diagrams without O
III] 1666 still allow us to define a SF-locus with some caveats.
Diagrams including C IV 1548,51 should be taken with caution
given the complexity of this doublet profile. Finally, we present a discussion
detailing the ISM conditions required to detect UV emission lines, visible only
in low gas-phase metallicity (12+log(O/H) ) and high ionization
parameter (log() ) environments. Overall, CLASSY and our UV
toolkit will be crucial in interpreting the spectra of the earliest galaxies
that JWST is currently revealing.Comment: 31 pages, submitted to ApJ, comments welcom
The COS Legacy Archive Spectroscopy SurveY (CLASSY) Treasury Atlas
Far-ultraviolet (FUV; ~1200-2000 angstroms) spectra are fundamental to our
understanding of star-forming galaxies, providing a unique window on massive
stellar populations, chemical evolution, feedback processes, and reionization.
The launch of JWST will soon usher in a new era, pushing the UV spectroscopic
frontier to higher redshifts than ever before, however, its success hinges on a
comprehensive understanding of the massive star populations and gas conditions
that power the observed UV spectral features. This requires a level of detail
that is only possible with a combination of ample wavelength coverage,
signal-to-noise, spectral-resolution, and sample diversity that has not yet
been achieved by any FUV spectral database.
We present the COS Legacy Spectroscopic SurveY (CLASSY) treasury and its
first high level science product, the CLASSY atlas. CLASSY builds on the HST
archive to construct the first high-quality (S/N_1500 >~ 5/resel),
high-resolution (R~15,000) FUV spectral database of 45 nearby (0.002 < z <
0.182) star-forming galaxies. The CLASSY atlas, available to the public via the
CLASSY website, is the result of optimally extracting and coadding 170
archival+new spectra from 312 orbits of HST observations.
The CLASSY sample covers a broad range of properties including stellar mass
(6.2 < logM_star(M_sol) < 10.1), star formation rate (-2.0 < log SFR (M_sol/yr)
< +1.6), direct gas-phase metallicity (7.0 < 12+log(O/H) < 8.8), ionization
(0.5 < O_32 < 38.0), reddening (0.02 < E(B-V < 0.67), and nebular density (10 <
n_e (cm^-3) < 1120). CLASSY is biased to UV-bright star-forming galaxies,
resulting in a sample that is consistent with z~0 mass-metallicity
relationship, but is offset to higher SFRs by roughly 2 dex, similar to z >~2
galaxies. This unique set of properties makes the CLASSY atlas the benchmark
training set for star-forming galaxies across cosmic time.Comment: Accepted for publication in Ap