scholarly journals Discovery of new dwarf galaxies around NGC4631 with Subaru/Hyper Suprime-Cam

2015 ◽  
Vol 11 (S317) ◽  
pp. 350-351
Author(s):  
Mikito Tanaka ◽  
Masashi Chiba ◽  
Yutaka Komiyama
Keyword(s):  
Local Group ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Outer Region ◽  
Absolute Magnitude ◽  
Effective Radius ◽  
The Other ◽  
Interacting Galaxies ◽  
Irregular Galaxy ◽  
Star Forming

AbstractWe have observed on-going interacting galaxies (NGC4631 and NGC4656) using Subaru/Hyper Suprime-Cam and reduced the data using HSC pipeline and conducted photometry based on DAOphot. Then, we have detected 8 new dwarf galaxy candidates in the outer region of NGC4631 and confirmed the three candidates previously reported by Karachentsev et al. 2014. The 3 or 4 candidates detected in this study may be a star-forming dwarf irregular galaxy and the other 7 candidates may be an old dwarf spheroidal galaxy based on these stellar populations. It looks like that the effective radius - absolute magnitude relation of dwarf galaxies in NGC4631 group is similar to the relation of the Local Group and the other galaxy systems.

scholarly journals Distance to the nearby dwarf galaxy [TT2009] 25 in the NGC 891 group using the tip of the red giant branch

2019 ◽  
Vol 629 ◽  
pp. L2 ◽  
Author(s):  
Oliver Müller ◽  
Rodrigo Ibata ◽  
Marina Rejkuba ◽  
Lorenzo Posti
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Small Scale ◽  
Accurate Information ◽  
Standard Candle ◽  
Stellar Halo ◽  
Red Giant ◽  
Small Field Of View

Dwarf galaxies are key objects for small-scale cosmological tests like the abundance problems or the planes-of-satellites problem. A crucial task is therefore to get accurate information for as many nearby dwarf galaxies as possible. Using extremely deep, ground-based V and i-band Subaru Suprime Cam photometry with a completeness of i = 27 mag, we measure the distance of the dwarf galaxy [TT2009] 25 using the tip of the red giant branch as a standard candle. This dwarf resides in the field around the Milky Way-analog NGC 891. Using a Bayesian approach, we measure a distance of 10.28−1.73+1.17 Mpc, which is consistent with the distance of NGC 891, and thus confirm it as a member of NGC 891. The dwarf galaxy follows the scaling relations defined by the Local Group dwarfs. We do not find an extended stellar halo around [TT2009] 25. In the small field of view of 100 kpc covered by the survey, only one bright dwarf galaxy and the giant stream are apparent. This is comparable to the Milky Way, where one bright dwarf resides in the same volume, as well as the Sagittarius stream – excluding satellites which are farther away but would be projected in the line-of-sight. It is thus imperative to survey for additional dwarf galaxies in a larger area around NGC 891 to test the abundance of dwarf galaxies and compare this to the number of satellites around the Milky Way.

Sardinia Radio Telescope (SRT) observations of Local Group dwarf galaxies

2017 ◽  
Vol 13 (S336) ◽  
pp. 109-112
Author(s):  
A. Tarchi ◽  
P. Castangia ◽  
G. Surcis ◽  
A. Brunthaler ◽  
K. M. Menten ◽  
...  
Keyword(s):  
Radio Telescope ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Radio Continuum ◽  
Maser Emission ◽  
Star Forming ◽  
Star Forming Regions ◽  
First Results ◽  
Ngc 6822 ◽  
Almost All

AbstractThe dwarf galaxies in the Local Group (LG) reveal a surprising amount of spatial structuring. In particular, almost all non-satellite dwarfs belong to one of two planes that show a very pronounced symmetry. In order to determine if these structures in the LG are dynamically stable or, alternatively, if they only represent transient alignments, proper motion measurements of these galaxies are required. A viable method to derive proper motions is offered by VLBI studies of 22-GHz water (and 6.7-GHz methanol) maser lines in star-forming regions.In 2016, in the framework of the Early Science Program of the Sardinia Radio Telescope (SRT), we have conducted an extensive observational campaign to map the entire optical body of all the LG dwarf galaxies that belong to the two planes, at C and K band, in a search for methanol and water maser emission.Here, we outline the project and present its first results on 3 targets, NGC 6822, IC 1613, and WLM. While no luminous maser emission has been detected in these galaxies, a number of interesting weaker detections has been obtained, associated with particularly active star forming regions. In addition, we have produced deep radio continuum maps for these galaxies, aimed at investigating their star forming activity and providing an improved assessment of star formation rates in these galaxies.

scholarly journals The dwarf galaxy satellite system of Centaurus A

2019 ◽  
Vol 629 ◽  
pp. A18 ◽  
Author(s):  
Oliver Müller ◽  
Marina Rejkuba ◽  
Marcel S. Pawlowski ◽  
Rodrigo Ibata ◽  
Federico Lelli ◽  
...  
Keyword(s):  
Luminosity Function ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
3D Structure ◽  
Major Axis ◽  
Asymptotic Giant Branch ◽  
Semi Major Axis ◽  
Distance Measurements ◽  
Red Giant

Dwarf galaxy satellite systems are essential probes to test models of structure formation, making it necessary to establish a census of dwarf galaxies outside of our own Local Group. We present deep FORS2 VI band images from the ESO Very Large Telescope (VLT) for 15 dwarf galaxy candidates in the Centaurus group of galaxies. We confirm nine dwarfs to be members of Cen A by measuring their distances using a Bayesian approach to determine the tip of the red giant branch luminosity. We have also fit theoretical isochrones to measure their mean metallicities. The properties of the new dwarfs are similar to those in the Local Group in terms of their sizes, luminosities, and mean metallicities. Within our photometric precision, there is no evidence of a metallicity spread, but we do observe possible extended star formation in several galaxies, as evidenced by a population of asymptotic giant branch stars brighter than the red giant branch tip. The new dwarfs do not show any signs of tidal disruption. Together with the recently reported dwarf galaxies by the complementary PISCeS survey, we study the luminosity function and 3D structure of the group. By comparing the observed luminosity function to the high-resolution cosmological simulation IllustrisTNG, we find agreement within a 90% confidence interval. However, Cen A seems to be missing its brightest satellites and has an overabundance of the faintest dwarfs in comparison to its simulated analogs. In terms of the overall 3D distribution of the observed satellites, we find that the whole structure is flattened along the line-of-sight, with a root-mean-square (rms) height of 130 kpc and an rms semi-major axis length of 330 kpc. Future distance measurements of the remaining dwarf galaxy candidates are needed to complete the census of dwarf galaxies in the Centaurus group.

A TREASURY STUDY OF STAR-FORMING REGIONS IN THE LOCAL GROUP. I.HSTPHOTOMETRY OF YOUNG POPULATIONS IN SIX DWARF GALAXIES

2012 ◽  
Vol 143 (3) ◽  
pp. 74 ◽  
Author(s):  
Luciana Bianchi ◽  
Boryana Efremova ◽  
Paul Hodge ◽  
Philip Massey ◽  
K. A. G. Olsen
Keyword(s):  
Local Group ◽  
Dwarf Galaxies ◽  
Star Forming ◽  
Star Forming Regions

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 Stars at Low Metallicity in Dwarf Galaxies

2008 ◽  
Vol 4 (S255) ◽  
pp. 310-317
Author(s):  
Eline Tolstoy ◽  
Giuseppina Battaglia ◽  
Andrew Cole
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Wide Field ◽  
Irregular Galaxy ◽  
First Stars ◽  
Field Spectroscopy ◽  
Low Metallicity

AbstractDwarf galaxies offer an opportunity to understand the properties of low metallicity star formation both today and at the earliest times at the epoch of the formation of the first stars. Here we concentrate on two galaxies in the Local Group: the dwarf irregular galaxy Leo A, which has been the recent target of deep HST/ACS imaging (Cole et al. 2007) and the Sculptor dwarf spheroidal, which has been the target of significant wide field spectroscopy with VLT/FLAMES (Battaglia 2007).

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 Sardinia Radio Telescope observations of Local Group dwarf galaxies – I. The cases of NGC 6822, IC 1613, and WLM

2019 ◽  
Vol 492 (1) ◽  
pp. 45-57
Author(s):  
A Tarchi ◽  
P Castangia ◽  
G Surcis ◽  
A Brunthaler ◽  
C Henkel ◽  
...  
Keyword(s):  
Local Group ◽  
Dwarf Galaxies ◽  
Radio Continuum ◽  
Star Forming ◽  
Star Forming Regions ◽  
Long Baseline ◽  
Planar Structures ◽  
Ngc 6822 ◽  
Almost All ◽  
Transient Alignment

ABSTRACT Almost all dwarf galaxies in the Local Group (LG) that are not satellites of the Milky Way or M 31 belong to either one of two highly symmetric planes. It is still a matter of debate whether these planar structures are dynamically stable or whether they only represent a transient alignment. Proper motions, if they could be measured, could help to discriminate between these scenarios. Such motions could be determined with multi-epoch very long baseline interferometry (VLBI) of sources that show emission from water and methanol at frequencies of 22 and 6.7 GHz, respectively. We report searches for such masers. We have mapped three LG galaxies, NGC 6822, IC 1613, and WLM, in the bands covering the water vapour and methanol lines. These systems are members of the two above-mentioned planes of galaxies. We have produced deep radio continuum (RC) maps and spectral line cubes. The former have been used to identify star-forming regions and to derive global galactic star formation rates (SFRs). These SFRs turn out to be lower than those determined at other wavelengths in two of our sources. This indicates that dwarf galaxies may follow predictions on the RC–SFR relation only in individual regions of enhanced RC emission, but not when considering the entire optical body of the sources. No methanol or water maser emission has been confidently detected, down to line luminosity limits of ∼4 × 10−3 and 10 × 10−3 L⊙, respectively. This finding is consistent with the small sizes, low SFRs, and metallicities of these galaxies.

scholarly journals NEW LIGHT IN STAR-FORMING DWARF GALAXIES: THE PMAS INTEGRAL FIELD VIEW OF THE BLUE COMPACT DWARF GALAXY Mrk 409

2009 ◽  
Vol 707 (2) ◽  
pp. 1676-1690 ◽  
Author(s):  
Luz M. Cairós ◽  
Nicola Caon ◽  
Polychronis Papaderos ◽  
Carolina Kehrig ◽  
Peter Weilbacher ◽  
...  
Keyword(s):  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Star Forming ◽  
Field View ◽  
Integral Field ◽  
Blue Compact Dwarf Galaxy

scholarly journals Solo dwarfs – III. Exploring the orbital origins of isolated Local Group galaxies with Gaia Data Release 2

2020 ◽  
Vol 501 (2) ◽  
pp. 2363-2377
Author(s):  
Alan W McConnachie ◽  
Clare R Higgs ◽  
Guillaume F Thomas ◽  
Kim A Venn ◽  
Patrick Côté ◽  
...  
Keyword(s):  
Milky Way ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Proper Motions ◽  
Star Forming ◽  
Isolated Galaxies ◽  
Data Release ◽  
Red Giant ◽  
Ngc 6822 ◽  
Interaction History

ABSTRACT We measure systemic proper motions for distant dwarf galaxies in the Local Group and investigate if these isolated galaxies have ever had an interaction with the Milky Way or M31. We cross-match photometry of isolated, star-forming, dwarf galaxies in the Local Group, taken as part of the Solo survey, with astrometric measurements from Gaia Data Release 2. We find that NGC 6822, Leo A, IC 1613, and WLM have sufficient supergiants with reliable astrometry to derive proper motions. An additional three galaxies (Leo T, Eridanus 2, and Phoenix) are close enough that their proper motions have already been derived using red giant branch stars. Systematic errors in Gaia DR2 are significant for NGC 6822, IC 1613, and WLM. We explore the orbits for these galaxies, and conclude that Phoenix, Leo A, and WLM are unlikely to have interacted with the Milky Way or M31, unless these large galaxies are very massive (${\gtrsim}1.6 \times 10^{12}\, \mathrm{M}_\odot$). We rule out a past interaction of NGC 6822 with M31 at ${\sim}99.99{{\ \rm per\ cent}}$ confidence, and find there is a &lt;10 per cent chance that NGC 6822 has had an interaction with the Milky Way. We examine the likely origins of NGC 6822 in the periphery of the young Local Group, and note that a future interaction of NGC 6822 with the Milky Way or M31 in the next 4 Gyr is essentially ruled out. Our measurements indicate that future Gaia data releases will provide good constraints on the interaction history for the majority of these galaxies.

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