scholarly journals A new distance to the Brick, the dense molecular cloud G0.253+0.016

2021 ◽  
Vol 502 (1) ◽  
pp. 1246-1252
Author(s):  
M Zoccali ◽  
E Valenti ◽  
F Surot ◽  
O A Gonzalez ◽  
A Renzini ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Near Infrared ◽  
Formation Rate ◽  
Dynamical Evolution ◽  
Galactic Centre ◽  
The Galaxy ◽  
Centre Region ◽  
Order Of Magnitude ◽  
Red Clump

ABSTRACT We analyse the near-infrared colour–magnitude diagram of a field including the giant molecular cloud G0.253+0.016 (a.k.a. The Brick) observed at high spatial resolution, with HAWK-I@VLT. The distribution of red clump stars in a line of sight crossing the cloud, compared with that in a direction just beside it, and not crossing it, allow us to measure the distance of the cloud from the Sun to be 7.20, with a statistical uncertainty of ±0.16 and a systematic error of ±0.20 kpc. This is significantly closer than what is generally assumed, i.e. that the cloud belongs to the near side of the central molecular zone, at 60 pc from the Galactic centre. This assumption was based on dynamical models of the central molecular zone, observationally constrained uniquely by the radial velocity of this and other clouds. Determining the true position of the Brick cloud is relevant because this is the densest cloud of the Galaxy not showing any ongoing star formation. This puts the cloud off by one order of magnitude from the Kennicutt–Schmidt relation between the density of the dense gas and the star formation rate. Several explanations have been proposed for this absence of star formation, most of them based on the dynamical evolution of this and other clouds, within the Galactic centre region. Our result emphasizes the need to include constraints coming from stellar observations in the interpretation of our Galaxy’s central molecular zone.

scholarly journals Simulating JWST deep extragalactic imaging surveys and physical parameter recovery

2020 ◽  
Vol 640 ◽  
pp. A67
Author(s):  
O. B. Kauffmann ◽  
O. Le Fèvre ◽  
O. Ilbert ◽  
J. Chevallard ◽  
C. C. Williams ◽  
...  
Keyword(s):  
Star Formation ◽  
Near Infrared ◽  
High Redshift ◽  
Spectral Energy Distribution ◽  
Formation Rate ◽  
Spectral Energy ◽  
Photometric Redshifts ◽  
The Galaxy ◽  
Stellar Masses ◽  
The Impact

We present a new prospective analysis of deep multi-band imaging with the James Webb Space Telescope (JWST). In this work, we investigate the recovery of high-redshift 5 <  z <  12 galaxies through extensive image simulations of accepted JWST programs, including the Early Release Science in the EGS field and the Guaranteed Time Observations in the HUDF. We introduced complete samples of ∼300 000 galaxies with stellar masses of log(M*/M⊙) > 6 and redshifts of 0 <  z <  15, as well as galactic stars, into realistic mock NIRCam, MIRI, and HST images to properly describe the impact of source blending. We extracted the photometry of the detected sources, as in real images, and estimated the physical properties of galaxies through spectral energy distribution fitting. We find that the photometric redshifts are primarily limited by the availability of blue-band and near-infrared medium-band imaging. The stellar masses and star formation rates are recovered within 0.25 and 0.3 dex, respectively, for galaxies with accurate photometric redshifts. Brown dwarfs contaminating the z >  5 galaxy samples can be reduced to < 0.01 arcmin−2 with a limited impact on galaxy completeness. We investigate multiple high-redshift galaxy selection techniques and find that the best compromise between completeness and purity at 5 <  z <  10 using the full redshift posterior probability distributions. In the EGS field, the galaxy completeness remains higher than 50% at magnitudes mUV <  27.5 and at all redshifts, and the purity is maintained above 80 and 60% at z ≤ 7 and 10, respectively. The faint-end slope of the galaxy UV luminosity function is recovered with a precision of 0.1–0.25, and the cosmic star formation rate density within 0.1 dex. We argue in favor of additional observing programs covering larger areas to better constrain the bright end.

scholarly journals Physics of a clumpy lensed galaxy at z = 1.6

2018 ◽  
Vol 619 ◽  
pp. A15 ◽  
Author(s):  
M. Girard ◽  
M. Dessauges-Zavadsky ◽  
D. Schaerer ◽  
J. Richard ◽  
K. Nakajima ◽  
...  
Keyword(s):  
Star Formation ◽  
Gravitational Lensing ◽  
Near Infrared ◽  
High Redshift ◽  
Formation Rate ◽  
Far Infrared ◽  
Rotating Disk ◽  
Cluster Galaxy ◽  
Star Forming ◽  
The Galaxy

Observations have shown that massive star-forming clumps are present in the internal structure of high-redshift galaxies. One way to study these clumps in detail with a higher spatial resolution is by exploiting the power of strong gravitational lensing which stretches images on the sky. In this work, we present an analysis of the clumpy galaxy A68-HLS115 at z = 1.5858, located behind the cluster Abell 68, but strongly lensed by a cluster galaxy member. Resolved observations with SINFONI/VLT in the near-infrared (NIR) show Hα, Hβ, [NII], and [OIII] emission lines. Combined with images covering the B band to the far-infrared (FIR) and CO(2–1) observations, this makes this galaxy one of the only sources for which such multi-band observations are available and for which it is possible to study the properties of resolved star-forming clumps and to perform a detailed analysis of the integrated properties, kinematics, and metallicity. We obtain a stability of υrot/σ0 = 2.73 by modeling the kinematics, which means that the galaxy is dominated by rotation, but this ratio also indicates that the disk is marginally stable. We find a high intrinsic velocity dispersion of 80 ± 10 km s−1 that could be explained by the high gas fraction of fgas = 0.75 ± 0.15 observed in this galaxy. This high fgas and the observed sSFR of 3.12 Gyr−1 suggest that the disk turbulence and instabilities are mostly regulated by incoming gas (available gas reservoir for star formation). The direct measure of the Toomre stability criterion of Qcrit = 0.70 could also indicate the presence of a quasi-stable thick disk. Finally, we identify three clumps in the Hα map which have similar velocity dispersions, metallicities, and seem to be embedded in the rotating disk. These three clumps contribute together to ∼40% on the SFRHα of the galaxy and show a star formation rate density about ∼100 times higher than HII regions in the local Universe.

scholarly journals The Close AGN Reference Survey (CARS)

2019 ◽  
Vol 627 ◽  
pp. A53 ◽  
Author(s):  
B. Husemann ◽  
J. Scharwächter ◽  
T. A. Davis ◽  
M. Pérez-Torres ◽  
I. Smirnova-Pinchukova ◽  
...  
Keyword(s):  
Star Formation ◽  
Near Infrared ◽  
Formation Rate ◽  
Broad Band ◽  
Host Galaxy ◽  
Radio Jets ◽  
Spatially Resolved ◽  
The Galaxy ◽  
Multi Phase ◽  
The Impact

Context. Galaxy-wide outflows driven by star formation and/or an active galactic nucleus (AGN) are thought to play a crucial rule in the evolution of galaxies and the metal enrichment of the inter-galactic medium. Direct measurements of these processes are still scarce and new observations are needed to reveal the nature of outflows in the majority of the galaxy population. Aims. We combine extensive, spatially-resolved, multi-wavelength observations, taken as part of the Close AGN Reference Survey (CARS), for the edge-on disc galaxy HE 1353−1917 in order to characterise the impact of the AGN on its host galaxy via outflows and radiation. Methods. Multi-color broad-band photometry was combined with spatially-resolved optical, near-infrared (NIR) and sub-mm and radio observations taken with the Multi-Unit Spectroscopy Explorer (MUSE), the Near-infrared Integral Field Spectrometer (NIFS), the Atacama Large Millimeter Array (ALMA), and the Karl G. Jansky Very Large Array (VLA) to map the physical properties and kinematics of the multi-phase interstellar medium. Results. We detect a biconical extended narrow-line region ionised by the luminous AGN orientated nearly parallel to the galaxy disc, extending out to at least 25 kpc. The extra-planar gas originates from galactic fountains initiated by star formation processes in the disc, rather than an AGN outflow, as shown by the kinematics and the metallicity of the gas. Nevertheless, a fast, multi-phase, AGN-driven outflow with speeds up to 1000 km s−1 is detected close to the nucleus at 1 kpc distance. A radio jet, in connection with the AGN radiation field, is likely responsible for driving the outflow as confirmed by the energetics and the spatial alignment of the jet and multi-phase outflow. Evidence for negative AGN feedback suppressing the star formation rate (SFR) is mild and restricted to the central kpc. But while any SFR suppression must have happened recently, the outflow has the potential to greatly impact the future evolution of the galaxy disc due to its geometrical orientation. Conclusions.. Our observations reveal that low-power radio jets can play a major role in driving fast, multi-phase, galaxy-scale outflows even in radio-quiet AGN. Since the outflow energetics for HE 1353−1917 are consistent with literature, scaling relation of AGN-driven outflows the contribution of radio jets as the driving mechanisms still needs to be systematically explored.

scholarly journals GALACTICNUCLEUS: A high angular-resolution JHKs imaging survey of the Galactic centre

2020 ◽  
Vol 641 ◽  
pp. A141
Author(s):  
F. Nogueras-Lara ◽  
R. Schödel ◽  
N. Neumayer ◽  
E. Gallego-Cano ◽  
B. Shahzamanian ◽  
...  
Keyword(s):  
Stellar Population ◽  
Near Infrared ◽  
Angular Resolution ◽  
Interstellar Extinction ◽  
Extinction Curve ◽  
Line Of Sight ◽  
Galactic Centre ◽  
High Angular Resolution ◽  
The Galaxy ◽  
Red Clump

Context. The characterisation of the extinction curve in the near-infrared (NIR) is fundamental to analysing the structure and stellar population of the Galactic centre (GC), whose analysis is hampered by the extreme interstellar extinction (AV ~ 30 mag) that varies on arc-second scales. Recent studies indicate that the behaviour of the extinction curve might be more complex than previously assumed, pointing towards a variation of the extinction curve as a function of wavelength. Aims. We aim to analyse the variations of the extinction index, α, with wavelength, line-of-sight, and absolute extinction, extending previous analyses to a larger area of the innermost regions of the Galaxy. Methods. We analysed the whole GALACTICNUCLEUS survey, a high-angular resolution (~0.2″) JHKs NIR survey specially designed to observe the GC in unprecedented detail. It covers a region of ~6000 pc2, comprising fields in the nuclear stellar disc, the inner bulge, and the transition region between them. We applied two independent methods based on red clump (RC) stars to constrain the extinction curve and analysed its variation superseding previous studies. Results. We used more than 165 000 RC stars and increased the size of the regions analysed significantly to confirm that the extinction curve varies with the wavelength. We estimated a difference Δα = 0.21 ± 0.07 between the obtained extinction indices, αJH = 2.44 ± 0.05 and αHKs = 2.23 ± 0.05. We also concluded that there is no significant variation of the extinction curve with wavelength, with the line-of-sight or the absolute extinction. Finally, we computed the ratios between extinctions, AJ∕AH = 1.87 ± 0.03 and AH/AKs = 1.84 ± 0.03, consistent with all the regions of the GALACTICNUCLEUS catalogue.

scholarly journals The Structure of the W49A Molecular Cloud Complex: Burst of Star Formation in the 105 M⊙ Core

1987 ◽  
Vol 115 ◽  
pp. 170-171
Author(s):  
Ryosuke Miyawaki ◽  
Masahiko Hayashi ◽  
Tetsuo Hasegawa
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Formation Rate ◽  
Maximum Level ◽  
Small Region ◽  
Sudden Increase ◽  
Core Mass ◽  
Order Of Magnitude ◽  
H Ii Region ◽  
Cloud Complex

We have observed the CS (J = 1-0), C34S (J = 1-0) and H51α emission toward the W49A molecular cloud complex in an area of 3'x 2′ (α x δ) with an angular resolution of 33″. The CS emitting region is 100″ x 80″ or 6.7 pc x 5.4 pc (α x δ) at the half maximum level. Although the CO emission is self-absorbed due to the foreground cold gas, the CS optical depth of the foreground gas is found to be small. Therefore, the two CS peaks at VLSR = 4 km s−1 and 12 km s−1 imply the presence of two dense molecular clouds toward W49A. The brighter 12 km s−1 cloud peaks 35″ southeast of W49A IRS, the infrared and H2O/OH maser sources associated with the compact H II region, while the 4 km s−1 cloud has a peak at W49A IRS. The hydrogen column density through the c34S emitting region is (0.3-1.7) x 1024 cm−2. The estimated core mass of the W49A molecular cloud is (0.5-2.5) x 104 M⊙. This mass is closely packed in a small region of 3.4 pc in diameter, and is about an order of magnitude larger than the virial mass of the system. The massive core will collapse within 10 years unless there is some special supporting mechanism. There was a sudden increase in the star formation rate 104– 105 years ago, suggesting a triggered burst of star formation in the core of W49A. The collision of two velocity clouds might have triggered the formation of this massive core and the burst of star formation.

scholarly journals The life cycle of the Central Molecular Zone – I. Inflow, star formation, and winds

2019 ◽  
Vol 490 (3) ◽  
pp. 4401-4418 ◽  
Author(s):  
Lucia Armillotta ◽  
Mark R Krumholz ◽  
Enrico M Di Teodoro ◽  
N M McClure-Griffiths
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Star Formation History ◽  
Galactic Centre ◽  
Two Phase ◽  
Star Forming ◽  
Stellar Feedback ◽  
Order Of Magnitude ◽  
Hydrodynamical Simulations

ABSTRACT We present a study of the gas cycle and star formation history in the central 500 pc of the Milky Way, known as Central Molecular Zone (CMZ). Through hydrodynamical simulations of the inner 4.5 kpc of our Galaxy, we follow the gas cycle in a completely self-consistent way, starting from gas radial inflow due to the Galactic bar, the channelling of this gas into a dense, star-forming ring/stream at ≈200–300 pc from the Galactic centre, and the launching of galactic outflows powered by stellar feedback. We find that star formation activity in the CMZ goes through oscillatory burst/quench cycles, with a period of tens to hundreds of Myr, characterized by roughly constant gas mass but order-of-magnitude level variations in the star formation rate. Comparison with the observed present-day star formation rate of the CMZ suggests that we are currently near a minimum of this cycle. Stellar feedback drives a mainly two-phase wind off the Galactic disc. The warm phase dominates the mass flux, and carries $100\!-\!200{{\ \rm per\ cent}}$ of the gas mass converted into stars. However, most of this gas goes into a fountain and falls back on to the disc rather than escaping the Galaxy. The hot phase carries most of the energy, with a time-averaged energy outflow rate of $10\!-\!20{{\ \rm per\ cent}}$ of the supernova energy budget.

scholarly journals Variability of the near-infrared extinction curve towards the Galactic centre

2019 ◽  
Vol 630 ◽  
pp. L3 ◽  
Author(s):  
F. Nogueras-Lara ◽  
R. Schödel ◽  
F. Najarro ◽  
A. T. Gallego-Calvente ◽  
E. Gallego-Cano ◽  
...  
Keyword(s):  
Near Infrared ◽  
Stellar Structure ◽  
Extinction Curve ◽  
Line Of Sight ◽  
Galactic Centre ◽  
High Angular Resolution ◽  
Mean Values ◽  
The Galaxy ◽  
Red Clump ◽  
Significant Line

Context. Due to the extreme extinction towards the Galactic centre (AV ∼ 30 mag), its stellar population is mainly studied in the near-infrared (NIR) regime. Therefore, a proper analysis of the NIR extinction curve is necessary to fully characterise the stellar structure and population of the inner part of the galaxy. Aims. We studied the dependence of the extinction index (αλ) in the NIR on the line of sight, wavelength, and extinction. Methods. We used the GALACTICNUCLEUS imaging survey, a high angular resolution catalogue (0.2″) for the inner part of the Galaxy in JHKs, and studied the spatial variation in the extinction index. We also applied two independent methods based on red clump stars to compute the extinction index between different bands and its variation with wavelength. Results. We did not detect any significant line-of-sight or extinction variation in α within the studied region in the nuclear stellar disc. The extinction index between JH and HKs differs by 0.19 ± 0.05. We obtained mean values for the extinction indices αJH = 2.43 ± 0.03 and αHKs = 2.23 ± 0.03. The dependence of the extinction index on the wavelength could explain the differences obtained for αλ in the literature since it was assumed constant for the NIR regime.

scholarly journals Using the Milky Way as a template for understanding star formation in extreme environments across cosmological timescales

2012 ◽  
Vol 8 (S292) ◽  
pp. 333-333
Author(s):  
Steven N. Longmore
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Formation Rate ◽  
Volume Density ◽  
Galactic Centre ◽  
Molecular Gas ◽  
Dense Gas ◽  
Star Forming ◽  
Star Formation Activity ◽  
The Galaxy

AbstractRecent surface- and volume-density star formation relations have been proposed which potentially unify our understanding of how gas is converted into stars, from the nearest star forming regions to ultra-luminous infrared galaxies. The inner 500 pc of our Galaxy – the Central Molecular Zone – contains the largest concentration of dense, high-surface density molecular gas in the Milky Way, providing an environment where the validity of these star-formation prescriptions can be tested.We have used recently-available data from HOPS, MALT90 and HiGAL at wavelengths where the Galaxy is transparent, to find the dense, star-forming molecular gas across the Milky Way [Longmore et al. (2012a), Longmore et al. (2012b)]. We use water and methanol maser emission to trace star formation activity within the last 105 years and 30 GHz radio continuum emission from the Wilkinson Microwave Anisotropy Satellite (WMAP) to estimate the high-mass star formation rate averaged over the last ∼ 4 × 106 years.We find the dense gas distribution is dominated by the very bright and spatially-extended emission within a few degrees of the Galactic centre [Purcell et al. (2012)]. This region accounts for ∼80% of the NH3(1,1) integrated intensity but only contains 4% of the survey area. However, in stark contrast, the distribution of star formation activity tracers is relatively uniform across the Galaxy.To probe the dense gas vs SFR relationship towards the Galactic centre region more quantitatively, we compared the HiGAL column density maps to the WMAP-derived SFR across the same region. The total mass and SFR derived using these methods agree well with previous values in the literature. The main conclusion from this analysis is that both the column-density threshold and volumetric SF relations over-predict the SFR by an order of magnitude given the reservoir of dense gas available to form stars. The region 1° < l < 3.5°, |b| < 0.5° is particular striking in this regard. It contains ∼107 M⊙ of dense molecular gas — enough to form 1000 Orion-like clusters — but the present-day star formation rate within this gas is only equivalent to that in Orion. This implication of this result is that any universal column/volume density relations must be a necessary but not sufficient condition for SF to occur.Understanding why such large reservoirs of dense gas deviate from commonly assumed SF relations is of fundamental importance and may help in the quest to understand SF in more extreme (dense) environments, like those found in interacting galaxies and at earlier epochs of the Universe.

scholarly journals CLEAR: The Gas-phase Metallicity Gradients of Star-forming Galaxies at 0.6 < z < 2.6

2021 ◽  
Vol 923 (2) ◽  
pp. 203
Author(s):  
Raymond C. Simons ◽  
Casey Papovich ◽  
Ivelina Momcheva ◽  
Jonathan R. Trump ◽  
Gabriel Brammer ◽  
...  
Keyword(s):  
Star Formation ◽  
Gas Phase ◽  
Near Infrared ◽  
Hubble Space Telescope ◽  
Formation Rate ◽  
Theoretical Models ◽  
Mass Range ◽  
Gravitational Potential Energy ◽  
Star Forming ◽  
The Galaxy

Abstract We report on the gas-phase metallicity gradients of a sample of 238 star-forming galaxies at 0.6 < z < 2.6, measured through deep near-infrared Hubble Space Telescope slitless spectroscopy. The observations include 12 orbit depth Hubble/WFC3 G102 grism spectra taken as a part of the CANDELS Lyα Emission at Reionization (CLEAR) survey, and archival WFC3 G102+G141 grism spectra overlapping the CLEAR footprint. The majority of galaxies in this sample are consistent with having a zero or slightly positive metallicity gradient (dZ/dR ≥ 0, i.e., increasing with radius) across the full mass range probed (8.5 < log M */M ⊙ < 10.5). We measure the intrinsic population scatter of the metallicity gradients, and show that it increases with decreasing stellar mass—consistent with previous reports in the literature, but confirmed here with a much larger sample. To understand the physical mechanisms governing this scatter, we search for correlations between the observed gradient and various stellar population properties at fixed mass. However, we find no evidence for a correlation with the galaxy properties we consider—including star formation rates, sizes, star formation rate surface densities, and star formation rates per gravitational potential energy. We use the observed weakness of these correlations to provide material constraints for predicted intrinsic correlations from theoretical models.

scholarly journals Near-infrared spectroscopic observations of massive young stellar object candidates in the central molecular zone

2018 ◽  
Vol 609 ◽  
pp. A109 ◽  
Author(s):  
G. Nandakumar ◽  
M. Schultheis ◽  
A. Feldmeier-Krause ◽  
R. Schödel ◽  
N. Neumayer ◽  
...  
Keyword(s):  
Star Formation ◽  
Near Infrared ◽  
Spectral Energy Distribution ◽  
Formation Rate ◽  
Initial Mass Function ◽  
Stellar Object ◽  
Spectral Energy ◽  
Galactic Centre ◽  
Late Type ◽  
Young Stellar Object

Context. The central molecular zone (CMZ) is a ~200 pc region around the Galactic centre. The study of star formation in the central part of the Milky Way is of great interest as it provides a template for the closest galactic nuclei. Aims. We present a spectroscopic follow-up of photometrically selected young stellar object (YSO) candidates in the CMZ of the Galactic centre. Our goal is to quantify the contamination of this YSO sample by reddened giant stars with circumstellar envelopes and to determine the star formation rate (SFR) in the CMZ. Methods. We obtained KMOS low-resolution near-infrared spectra (R ~ 4000) between 2.0 and 2.5 μm of sources, many of which have been previously identified by mid-infrared photometric criteria as massive YSOs in the Galactic centre. Our final sample consists of 91 stars with good signal-to-noise ratio. We separated YSOs from cool late-type stars based on spectral features of CO and Brγ at 2.3 μm and 2.16 μm, respectively. We made use of spectral energy distribution (SED) model fits to the observed photometric data points from 1.25 to 24 μm to estimate approximate masses for the YSOs. Results. Using the spectroscopically identified YSOs in our sample, we confirm that existing colour–colour diagrams and colour-magnitude diagrams are unable to efficiently separate YSOs and cool late-type stars. In addition, we define a new colour–colour criterion that separates YSOs from cool late-type stars in the H−KS vs. H −[8.0] diagram. We use this new criterion to identify YSO candidates in the |l| < 1.̊5, |b| < 0.̊5, region and use model SED fits to estimate their approximate masses. By assuming an appropriate initial mass function (IMF) and extrapolating the stellar IMF down to lower masses, we determine a SFR of ~0.046 ± 0.026 M⊙ yr-1 assuming an average age of 0.75 ± 0.25 Myr for the YSOs. This value is lower than estimates found using the YSO counting method in the literature. Conclusions. Our SFR estimate in the CMZ agrees with the previous estimates from various methods and reaffirms that star formation in the CMZ is proceeding at a lower rate than predicted by various star forming models.

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