scholarly journals Dissecting star formation in the “Atoms-for-Peace” galaxy

2018 ◽  
Vol 614 ◽  
pp. A130 ◽  
Author(s):  
K. George ◽  
P Joseph ◽  
P. Côté ◽  
S. K. Ghosh ◽  
J. B. Hutchings ◽  
...  
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Initial Conditions ◽  
Dwarf Galaxy ◽  
Main Body ◽  
Star Forming ◽  
Uv Imaging ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Tidal Tails

Context. The tidal tails of post-merger galaxies exhibit ongoing star formation far from their disks. The study of such systems can be useful for our understanding of gas condensation in diverse environments. Aims. The ongoing star formation in the tidal tails of post-merger galaxies can be directly studied from ultraviolet (UV) imaging observations. Methods. The post merger galaxy NGC7252 (“Atoms-for-Peace” galaxy) is observed with the Astrosat UV imaging telescope (UVIT) in broadband NUV and FUV filters to isolate the star-forming regions in the tidal tails and study the spatial variation in star formation rates. Results. Based on ultraviolet imaging observations, we discuss star-forming regions of ages <200 Myr in the tidal tails. We measure star formation rates in these regions and in the main body of the galaxy. The integrated star formation rate (SFR) of NGC7252 (i.e., that in the galaxy and tidal tails combined) without correcting for extinction is found to be 0.81 ± 0.01 M⊙ yr−1. We show that the integrated SFR can change by an order of magnitude if the extinction correction used in SFR derived from other proxies are taken into consideration. The star formation rates in the associated tidal dwarf galaxies (NGC7252E, SFR = 0.02 M⊙ yr−1 and NGC7252NW, SFR = 0.03 M⊙ yr−1) are typical of dwarf galaxies in the local Universe. The spatial resolution of the UV images reveals a gradient in star formation within the tidal dwarf galaxy. The star formation rates show a dependence on the distance from the centre of the galaxy. This can be due to the different initial conditions responsible for the triggering of star formation in the gas reservoir that was expelled during the recent merger in NGC7252.

scholarly journals Star-forming regions in the intragroup medium of compact groups of galaxies

2009 ◽  
Vol 5 (S262) ◽  
pp. 440-441
Author(s):  
S. Torres-Flores ◽  
C. Mendes de Oliveira ◽  
D. F. de Mello ◽  
P. Amram ◽  
H. Plana ◽  
...  
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Early Stage ◽  
Velocity Fields ◽  
Compact Groups ◽  
Advanced Stage ◽  
Groups Of Galaxies ◽  
Star Forming ◽  
Star Forming Regions ◽  
Fabry Perot

AbstractWe present the results of a multiwavelength campaign searching for young objects in the intragroup medium of seven compact groups of galaxies: HCG 2, 7, 22, 23, 92, 100 and NGC 92. We used Fabry-Perot velocity fields and rotation curves together with GALEX NUV and FUV images, optical R-band and HI maps to evaluate the stage of interaction of each group. We conclude that groups (i) HCG 7 and HCG 23 are in an early stage of interaction, (ii) HCG 2 and HCG 22 are mildly interacting, and (iii) HCG 92, HCG 100 and NGC 92 are in a late stage of evolution. Evolved groups have a population of young objects in their intragroup medium while no such population is found within the less evolved groups. We also report the discovery of a tidal dwarf galaxy candidate in the tail of NGC 92. These three groups, besides containing galaxies which have peculiar velocity fields, also show extended HI tails. Our results indicate that the advanced stage of evolution of a group together with the presence of intragroup HI clouds may lead to star formation in the intragroup medium.

scholarly journals A Gaseous Group with Unusual Remote Star Formation

2011 ◽  
Vol 28 (3) ◽  
pp. 271-279 ◽  
Author(s):  
N. Santiago-Figueroa ◽  
M. E. Putman ◽  
J. Werk ◽  
G. R. Meurer ◽  
E. Ryan-Weber
Keyword(s):  
Star Formation ◽  
Spiral Galaxy ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Spiral Arms ◽  
Gaseous Disk ◽  
Ram Pressure ◽  
The Galaxy ◽  
Galaxy Center ◽  
Region 10

AbstractWe present VLA 21-cm observations of the spiral galaxy ESO 481-G017 to determine the nature of remote star formation traced by an Hii region found 43 kpc and ∼800 km s−1 from the galaxy center (in projection). ESO 481-G017 is found to have a 120 kpc Hi disk with a mass of 1.2 × 1010M⊙ and UV GALEX images reveal spiral arms extending into the gaseous disk. Two dwarf galaxies with Hi masses close to 108M⊙ are detected at distances of ∼200 kpc from ESO 481-G017 and a Hi cloud with a mass of 6 × 107M⊙ is found near the position and velocity of the remote Hii region. The Hii region is somewhat offset from the Hi cloud spatially and there is no link to ESO 481-G017 or the dwarf galaxies. We consider several scenarios for the origin of the cloud and Hii region and find the most likely is a dwarf galaxy that is undergoing ram pressure stripping. The Hi mass of the cloud and Hi luminosity of the Hii region (1038.1 erg s−1) are consistent with dwarf galaxy properties, and the stripping can trigger the star formation as well as push the gas away from the stars.

scholarly journals Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas

2020 ◽  
Vol 643 ◽  
pp. A141 ◽  
Author(s):  
S. C. Madden ◽  
D. Cormier ◽  
S. Hony ◽  
V. Lebouteiller ◽  
N. Abel ◽  
...  
Keyword(s):  
Star Formation ◽  
Mass Fraction ◽  
Conversion Factor ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Molecular Gas ◽  
Star Forming ◽  
Forming Efficiency ◽  
Low Metallicity ◽  
Co Observations

Context. Molecular gas is a necessary fuel for star formation. The CO (1−0) transition is often used to deduce the total molecular hydrogen but is challenging to detect in low-metallicity galaxies in spite of the star formation taking place. In contrast, the [C II]λ158 μm is relatively bright, highlighting a potentially important reservoir of H2 that is not traced by CO (1−0) but is residing in the C+-emitting regions. Aims. Here we aim to explore a method to quantify the total H2 mass (MH2) in galaxies and to decipher what parameters control the CO-dark reservoir. Methods. We present Cloudy grids of density, radiation field, and metallicity in terms of observed quantities, such as [O I], [C I], CO (1−0), [C II], LTIR, and the total MH2. We provide recipes based on these models to derive total MH2 mass estimates from observations. We apply the models to the Herschel Dwarf Galaxy Survey, extracting the total MH2 for each galaxy, and compare this to the H2 determined from the observed CO (1−0) line. This allows us to quantify the reservoir of H2 that is CO-dark and traced by the [C II]λ158 μm. Results. We demonstrate that while the H2 traced by CO (1−0) can be negligible, the [C II]λ158 μm can trace the total H2. We find 70 to 100% of the total H2 mass is not traced by CO (1−0) in the dwarf galaxies, but is well-traced by [C II]λ158 μm. The CO-dark gas mass fraction correlates with the observed L[C II]/LCO(1−0) ratio. A conversion factor for [C II]λ158 μm to total H2 and a new CO-to-total-MH2 conversion factor as a function of metallicity are presented. Conclusions. While low-metallicity galaxies may have a feeble molecular reservoir as surmised from CO observations, the presence of an important reservoir of molecular gas that is not detected by CO can exist. We suggest a general recipe to quantify the total mass of H2 in galaxies, taking into account the CO and [C II] observations. Accounting for this CO-dark H2 gas, we find that the star-forming dwarf galaxies now fall on the Schmidt–Kennicutt relation. Their star-forming efficiency is rather normal because the reservoir from which they form stars is now more massive when introducing the [C II] measures of the total H2 compared to the small amount of H2 in the CO-emitting region.

scholarly journals The curious case of the companion: evidence for cold accretion onto a dwarf satellite near the isolated elliptical NGC 7796

2018 ◽  
Vol 620 ◽  
pp. A133 ◽  
Author(s):  
T. Richtler ◽  
M. Hilker ◽  
K. Voggel ◽  
T. H. Puzia ◽  
R. Salinas ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
Dwarf Galaxy ◽  
Broad Band ◽  
Hii Regions ◽  
Diagnostic Tools ◽  
Strong Line ◽  
Main Body ◽  
Surprising Result ◽  
Star Forming ◽  
The Galaxy

Context. The isolated elliptical (IE) NGC 7796 is accompanied by an interesting early-type dwarf galaxy, named NGC 7796-DW1. It exhibits a tidal tail, very boxy isophotes, and multiple nuclei or regions (A, B, and C) that are bluer than the bulk population of the galaxy, indicating a younger age. These properties are suggestive of a dwarf–dwarf merger remnant. Aims. Dwarf–dwarf mergers are poorly understood, but may have a high importance for dwarf galaxy evolution. We want to investigate the properties of the dwarf galaxy and its components to find more evidence for a dwarf–dwarf merger or for alternative formation scenarios. Methods. We use the Multi-Unit Spectroscopic Explorer (MUSE) at the VLT to investigate NGC 7796-DW1. We extract characteristic spectra to which we apply the STARLIGHT population synthesis software to obtain ages and metallicities of the various population components of the galaxy. This permits us to isolate the emission lines for which fluxes and flux ratios can be measured and to which strong-line diagnostic tools can be applied. Results. The galaxy’s main body is old and metal-poor. A surprising result is the extended line emission in the galaxy, forming a ring-like structure with a projected diameter of 2.2 kpc. The line ratios fall into the regime of HII-regions, although OB-stellar populations cannot be identified by spectral signatures. The low Hα surface brightnesses indicate unresolved star-forming substructures, which means that broad-band colours are not reliable age or metallicity indicators. Nucleus A is a relatively old (7 Gyr or older) and metalpoor super star cluster, most probably the nucleus of the dwarf, now displaced. The star-forming regions B and C show younger and distinctly more metal-rich components. The emission line ratios of regions B and C indicate an almost solar oxygen abundance, if compared with radiation models of HII regions. Oxygen abundances from empirical calibrations point to only half-solar. The ring-like Hα-structure does not exhibit signs of rotation or orbital movements. Conclusions. NGC 7796-DW1 occupies a particular role in the group of transition-type galaxies with respect to its origin and current evolutionary state, being the companion of an IE. The dwarf–dwarf merger scenario is excluded because of the missing metal-rich merger component. A viable alternative is gas accretion from a reservoir of cold, metal-rich gas. NGC 7796 has to provide this gas within its X-ray bright halo. As illustrated by NGC 7796-DW1, cold accretion may be a general solution to the problem of extended star formation histories in transition dwarf galaxies.

scholarly journals Impact of metallicity and star formation rate on the time-dependent, galaxy-wide stellar initial mass function

2018 ◽  
Vol 620 ◽  
pp. A39 ◽  
Author(s):  
T. Jeřábková ◽  
A. Hasani Zonoozi ◽  
P. Kroupa ◽  
G. Beccari ◽  
Z. Yan ◽  
...  
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Probability Density Distribution ◽  
Star Forming ◽  
The Galaxy ◽  
Stellar Initial Mass Function ◽  
Stellar Masses

The stellar initial mass function (IMF) is commonly assumed to be an invariant probability density distribution function of initial stellar masses. These initial stellar masses are generally represented by the canonical IMF, which is defined as the result of one star formation event in an embedded cluster. As a consequence, the galaxy-wide IMF (gwIMF) should also be invariant and of the same form as the canonical IMF; gwIMF is defined as the sum of the IMFs of all star-forming regions in which embedded clusters form and spawn the galactic field population of the galaxy. Recent observational and theoretical results challenge the hypothesis that the gwIMF is invariant. In order to study the possible reasons for this variation, it is useful to relate the observed IMF to the gwIMF. Starting with the IMF determined in resolved star clusters, we apply the IGIMF-theory to calculate a comprehensive grid of gwIMF models for metallicities, [Fe/H] ∈ (−3, 1), and galaxy-wide star formation rates (SFRs), SFR ∈ (10−5, 105) M⊙ yr−1. For a galaxy with metallicity [Fe/H] < 0 and SFR > 1 M⊙ yr−1, which is a common condition in the early Universe, we find that the gwIMF is both bottom light (relatively fewer low-mass stars) and top heavy (more massive stars), when compared to the canonical IMF. For a SFR < 1 M⊙ yr−1 the gwIMF becomes top light regardless of the metallicity. For metallicities [Fe/H] > 0 the gwIMF can become bottom heavy regardless of the SFR. The IGIMF models predict that massive elliptical galaxies should have formed with a gwIMF that is top heavy within the first few hundred Myr of the life of the galaxy and that it evolves into a bottom heavy gwIMF in the metal-enriched galactic centre. Using the gwIMF grids, we study the SFR−Hα relation and its dependency on metallicity and the SFR. We also study the correction factors to the Kennicutt SFRK − Hα relation and provide new fitting functions. Late-type dwarf galaxies show significantly higher SFRs with respect to Kennicutt SFRs, while star-forming massive galaxies have significantly lower SFRs than hitherto thought. This has implications for gas-consumption timescales and for the main sequence of galaxies. We explicitly discuss Leo P and ultra-faint dwarf galaxies.

scholarly journals Study of the Milky Way's hot coronal gas with its dwarf galaxies

2015 ◽  
Vol 11 (S317) ◽  
pp. 340-341
Author(s):  
Stefano Pasetto ◽  
Mark Cropper ◽  
Yutaka Fujita ◽  
Cesare Chiosi ◽  
Eva K. Grebel
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Stellar System ◽  
Analytical Framework ◽  
Host Galaxy ◽  
Star Forming ◽  
Star Forming Regions ◽  
Tidal Forces ◽  
Diffuse Halo ◽  
Analytical Criterion

AbstractA large amount (5 × 1010 M⊙) of hot gas is thought to exist in an extended (≈ 200 kpc) hot diffuse halo around the Milky Way. We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation of this gravitationally bound systems in this external environment. Ram pressure, Kelvin-Helmholtz and Rayleigh- Taylor instabilities, and tidal forces are accounted for separately in an analytical framework and compared in their role in influencing the star forming regions. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment, useful in observational applications as well as theoretical interpretations of numerical results. We consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams (CMDs) of the orbiting system, thus investigating the detectability limits and relevance of these different effects for future observational projects. The theoretical framework developed has direct applications to the cases of our MW system as well as dwarf galaxies in galaxy clusters or any primordial gas-rich star cluster of stars orbiting within its host galaxy.

scholarly journals Ionized and neutral gas in the XUV discs of nearby spiral galaxies

2014 ◽  
Vol 10 (S309) ◽  
pp. 65-68
Author(s):  
López-Sánchez ◽  
B. S. Koribalski ◽  
T. Westmeier ◽  
C. Esteban
Keyword(s):  
Spiral Galaxies ◽  
Dwarf Galaxy ◽  
Chemical Abundances ◽  
Ionized Gas ◽  
Galaxy Interactions ◽  
Star Forming ◽  
Star Forming Regions ◽  
Neutral Gas ◽  
The Galaxy ◽  
Nearby Galaxies

AbstractWe are conducting a multiwavelength study of XUV discs in nearby, gas-rich spiral galaxies combining the available UV (GALEX) observations with H i data obtained at the ATCA as part of the Local Volume HI Survey (LVHIS) project and multi-object fibre spectroscopy obtained using the 2dF/AAOmega instrument at the 3.9m AAT. Here we present the results of the multiwavelength analysis of the galaxy pair NGC 1512/1510. The H i distribution of NGC 1512 is very extended with two pronounced spiral/tidal arms. Hundreds of independent UV-bright regions are associated with dense H i clouds in the galaxy outskirts. We confirm the detection of ionized gas in the majority of them and characterize their physical properties, chemical abundances and kinematics. Both the gas distribution andthe distribution of the star-forming regions are affected by gravitational interactionwith the neighbouring blue compact dwarf galaxy NGC 1510. Our multiwavelength analysis provides new clues about local star-formation processes, the metal redistribution in the outer gaseous discs of spiral galaxies, the importance of galaxy interactions, the fate of the neutral gas and the chemical evolution in nearby galaxies.

scholarly journals Unravelling the enigmatic ISM conditions in Minkowski’s object

2020 ◽  
Vol 499 (4) ◽  
pp. 4940-4960
Author(s):  
Henry R M Zovaro ◽  
Robert Sharp ◽  
Nicole P H Nesvadba ◽  
Lisa Kewley ◽  
Ralph Sutherland ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Dwarf Galaxy ◽  
Formation Rate ◽  
Theoretical Models ◽  
Strong Line ◽  
Valuable Insight ◽  
Jet Interaction ◽  
Star Forming ◽  
The Galaxy

ABSTRACT Local examples of jet-induced star formation lend valuable insight into its significance in galaxy evolution and can provide important observational constraints for theoretical models of positive feedback. Using optical integral field spectroscopy, we present an analysis of the ISM conditions in Minkowski’s object (z = 0.0189), a peculiar star-forming dwarf galaxy located in the path of a radio jet from the galaxy NGC 541. Full spectral fitting with ppxf indicates that Minkowski’s object primarily consists of a young stellar population $\sim \! 10\, \rm Myr$ old, confirming that the bulk of the object’s stellar mass formed during a recent jet interaction. Minkowski’s object exhibits line ratios largely consistent with star formation, although there is evidence for a low level ($\lesssim \! 15 \, \rm per \, cent$) of contamination from a non-stellar ionizing source. Strong-line diagnostics reveal a significant variation in the gas-phase metallicity within the object, with $\log \left(\rm O / H \right) + 12$ varying by $\sim \! 0.5\, \rm dex$, which cannot be explained by in-situ star formation, an enriched outflow from the jet, or enrichment of gas in the stellar bridge between NGC 541 and NGC 545/547. We hypothesize that Minkowski’s object either (i) was formed as a result of jet-induced star formation in pre-existing gas clumps in the stellar bridge, or (ii) is a gas-rich dwarf galaxy that is experiencing an elevation in its star formation rate due to a jet interaction, and will eventually redden and fade, becoming an ultradiffuse galaxy as it is processed by the cluster.

scholarly journals Star-forming complexes in the polar ring galaxy NGC660

2017 ◽  
Vol 26 (1) ◽  
Author(s):  
Ksenia I. Smirnova ◽  
Dmitri S. Wiebe ◽  
Alexei V. Moiseev
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Star Forming ◽  
Polar Ring ◽  
Star Forming Regions ◽  
Disk Star ◽  
Dust Mass ◽  
The Galaxy ◽  
Galaxy Disk

AbstractGalaxies with polar rings consist of two subsystems, a disk and a ring, which rotate almost in orthogonal planes. In this paper, we analyze the parameters characterizing the composition of the interstellar medium and star formation in star-forming complexes belonging to polar ring galaxy NGC660. We show that star-forming regions in the ring of the galaxy are distinctly different from those in the galaxy disk. They possess substantially lower infrared luminosities, which is indicative of less dust mass in these regions than in a typical disk star-forming region. UV and Hα luminosities also appear to be lower in the ring, which is likely a consequence of its relatively recent formation.

scholarly journals The host galaxy of GRB 980425/SN1998bw: a collisional ring galaxy

2019 ◽  
Vol 485 (4) ◽  
pp. 5411-5422 ◽  
Author(s):  
M Arabsalmani ◽  
S Roychowdhury ◽  
T K Starkenburg ◽  
L Christensen ◽  
E Le Floc’h ◽  
...  
Keyword(s):  
Star Formation ◽  
Gamma Ray ◽  
Dwarf Galaxy ◽  
Formation Rate ◽  
Host Galaxy ◽  
Gamma Ray Burst ◽  
Star Forming ◽  
Star Forming Regions ◽  
Very Large Telescope ◽  
Companion Galaxy

ABSTRACT We report Giant Metrewave Radio Telescope (GMRT), Very Large Telescope (VLT), and Spitzer Space Telescope observations of ESO 184−G82, the host galaxy of GRB 980425/SN 1998bw, that yield evidence of a companion dwarf galaxy at a projected distance of 13 kpc. The companion, hereafter GALJ193510-524947, is a gas-rich, star-forming galaxy with a star formation rate of $\rm 0.004\, M_{\odot }\, yr^{-1}$, a gas mass of $10^{7.1\pm 0.1} \, \mathrm{M}_{\odot}$, and a stellar mass of $10^{7.0\pm 0.3} \, \mathrm{M}_{\odot}$. The interaction between ESO 184−G82 and GALJ193510-524947 is evident from the extended gaseous structure between the two galaxies in the GMRT H i 21 cm map. We find a ring of high column density H i gas, passing through the actively star-forming regions of ESO 184−G82 and the GRB location. This ring lends support to the picture in which ESO 184−G82 is interacting with GALJ193510-524947. The massive stars in GALJ193510-524947 have similar ages to those in star-forming regions in ESO 184−G82, also suggesting that the interaction may have triggered star formation in both galaxies. The gas and star formation properties of ESO 184−G82 favour a head-on collision with GALJ193510-524947 rather than a classical tidal interaction. We perform state-of-the-art simulations of dwarf–dwarf mergers and confirm that the observed properties of ESO 184−G82 can be reproduced by collision with a small companion galaxy. This is a very clear case of interaction in a gamma-ray burst host galaxy and of interaction-driven star formation giving rise to a gamma-ray burst in a dense environment.

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