Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Dwarf galaxies”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Brought to Light. I. Quantification of Disk Substructure in Dwarf Early-type Galaxies

Dwarf early-type galaxies (ETGs) display a rich diversity in their photometric, structural, and dynamical properties. In this work, we address their structural complexity by studying with deep imaging a sample of nine dwarf ETGs from the Virgo galaxy cluster, characterized by having faint disk features such as bars and spiral arms, that lie mostly hidden within the bright diffuse light of the galaxies. We present a new, robust method that aims to identify and extract the disk substructure embedded in these dwarf ETGs. The method consists in an iterative procedure that gradually separates a galaxy image into two components: the bright, dominant, diffuse component, and the much fainter, underlying disk component. By applying it to the dwarf ETG sample, we quantify their disk substructure and find that its relative contribution to the total galaxy light ranges between 2.2% and 6.4% within two effective radii. We test the reliability of the method, and prove that it is accurate in recovering the disk substructure we introduce in mock galaxy images, even at low disk-to-total light fractions of a few percent. As a potential application of the method, we perform a Fourier analysis on the extracted disk substructures and measure the orientation, length, and strength of the bars, as well as the pitch angle and strength of the spiral arms. We also briefly discuss a scenario based on the numerical simulations presented in our companion paper, Brought to Light II: Smith et al., in which we investigate the origins of the substructure in such dwarf systems.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Dwarf spheroidal galaxies: Keystones of galaxy evolution

Dwarf spheroidal galaxies are the most insignificant extragalactic stellar systems in terms of their visibility, but potentially very significant in terms of their role in the formation and evolution of much more luminous galaxies. We discuss the present observational data and their implications for theories of the formation and evolution of both dwarf and giant galaxies. The putative dark-matter content of these low-surface-brightness systems is of particular interest, as is their chemical evolution. Surveys for new dwarf spheroidals hidden behind the stars of our Galaxy and those which are not bound to giant galaxies may give new clues as to the origins of this unique class of galaxy.

Gallagher, John S., III↗
DOE OSTI2021

Spectroscopic Confirmation of the Sixth Globular Cluster in the Fornax Dwarf Spheroidal Galaxy*

The Fornax dwarf spheroidal galaxy has an anomalous number of globular clusters, five, for its stellar mass. There is a longstanding debate about a potential sixth globular cluster (Fornax 6) that has recently been "rediscovered" in DECam imaging. We present new Magellan/M2FS spectroscopy of the Fornax 6 cluster and Fornax dSph. Combined with literature data we identify ~15–17 members of the Fornax 6 cluster, showing that this overdensity is indeed a star cluster and associated with the Fornax dSph. The cluster is significantly more metal-rich (mean metallicity of $\overline{[\mathrm{Fe}/{\rm{H}}]}$ = –0.71 ± 0.05) than the other five Fornax globular clusters (–2.5 < [Fe/H] < –1.4) and more metal-rich than the bulk of Fornax. We measure a velocity dispersion of ${5.6}_{-1.6}^{+2.0}\mathrm{km}\,{{\rm{s}}}^{-1}$ corresponding to an anomalously high mass-to-light of 15 < M/L < 258 at 90% confidence when calculated assuming equilibrium. Two stars inflate this dispersion and may be either Fornax field stars or as yet unresolved binary stars. Alternatively, the Fornax 6 cluster may be undergoing tidal disruption. Based on its metal-rich nature, the Fornax 6 cluster is likely younger than the other Fornax clusters, with an estimated age of ~2 Gyr when compared to stellar isochrones. The chemodynamics and star formation history of Fornax shows imprints of major events such as infall into the Milky Way, multiple pericenter passages, star formation bursts, and/or potential mergers or interactions. Any of these events may have triggered the formation of the Fornax 6 cluster.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1988

A bimodal model for the galaxy luminosity function

The galaxy luminosity function in the Virgo cluster has been recently found to show a clear separation between bright galaxies and dwarf galaxies. Here, consideration is given to the effect on the luminosity function of galaxy binding energy which allows gas to be retained and star formation to proceed over about 1 Gyr in massive galaxies, but implies wind-driven mass loss and inefficient star formation in dwarf galaxies.

Schaeffer, R.↗
DOE OSTI2021

Distance and Mass of the NGC 253 Galaxy Group

Two dwarf galaxies, WOC2017-07 and PGC 704814, located in the vicinity of the nearby luminous spiral galaxy NGC 253 were observed with the Advanced Camera for Surveys on the Hubble Space Telescope. Their distances of 3.62 ± 0.18 Mpc and 3.66 ± 0.18 Mpc were derived using the tip of the red giant branch method. These distances are consistent with the dwarf galaxies being members of the NGC 253 group. Based on the radial velocities and projected separations of seven assumed dwarf companions, we estimated the total mass of NGC 253 to be (8.1 ± 2.6)10{sup 11} M {sub ⊙}, giving a total-mass-to-K-luminosity ratio of M {sub orb}/L {sub K} = (8.5 ± 2.7)M {sub ⊙}/L {sub ⊙}. A notable property of NGC 253 is its declined rotation curve. NGC 253 joins four other luminous spiral galaxies in the Local Volume with declined rotation curves (NGC 2683, NGC 2903, NGC 3521, and NGC 5055) that together have the low average total-mass-to-luminosity ratio, M {sub orb}/L {sub K} = (5.5 ± 1.1)M {sub ⊙}/L {sub ⊙}. This value is only ∼1/5 of the corresponding ratio for the Milky Way and M31.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

A Search for Faint Resolved Galaxies Beyond the Milky Way in DES Year 6: A New Faint, Diffuse Dwarf Satellite of NGC 55

We report results from a systematic wide-area search for faint dwarf galaxies at heliocentric distances from 0.3 to 2 Mpc using the full 6 yr of data from the Dark Energy Survey (DES). Unlike previous searches over the DES data, this search specifically targeted a field population of faint galaxies located beyond the Milky Way virial radius. We derive our detection efficiency for faint, resolved dwarf galaxies in the Local Volume with a set of synthetic galaxies and expect our search to be complete to M$_{V}$ ∼ (−7, −10) mag for galaxies at D = (0.3, 2.0) Mpc. We find no new field dwarfs in the DES footprint, but we report the discovery of one high-significance candidate dwarf galaxy at a distance of , a potential satellite of the Local Volume galaxy NGC 55, separated by 47′ (physical separation as small as 30 kpc). We estimate this dwarf galaxy to have an absolute V-band magnitude of and an azimuthally averaged physical half-light radius of , making this one of the lowest surface brightness galaxies ever found with . This is the largest, most diffuse galaxy known at this luminosity, suggesting possible tidal interactions with its host.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

An X-ray image of the Fornax dwarf spheroidal galaxy

A ROSAT X-ray observation of the Fornax dwarf spheroidal galaxy is presented. A total of 19 sources are identified, one of which is a probable background galaxy cluster. This is consistent with the number expected due to the extragalactic background. Scaling in luminosity from normal ellipticals and bulges, we would expect to see at most one accreting binary source. This is consistent with our results, and implies that the IMF was not heavily biased towards massive stars. Scaling instead from globular clusters, we would expect eight sources in Fornax in the energy range 10 exp 36 - 10 exp 38 erg/s. We observe none. The low-density environment of the dwarf galaxy evidently does not produce a population of accreting neutron stars through star-star collisions. We place an upper limit of 4 x 10 exp -12 erg sq cm s on any diffuse gas component, corresponding to 10 exp 5 solar mass of gas at 107 K. However, if heated to X-ray temperatures, gas could escape Fornax.

Gizis, J. E.↗
NASA NTRS1982

Photometry of resolved galaxies. I - The Pegasus dwarf irregular

Color-magnitude diagrams for resolved stars in the Pegasus dwarf galaxy in the green, red, and infrared passbands of the extended Gunn photometric system are presented. The evolved nature of the upper main sequence and the lack of luminous red supergiants indicate that recent star formation in Pegasus has been very subdued. Three star clusters are identified. Their red colors indicate they are of intermediate age or older. Two features of the color-magnitude diagrams are of interest: a group of red stars with I at about 21.3, which may be the counterparts of the carbon stars found in the Magellanic Clouds, and a clump in the (I, R-I)-diagram, which is probably the tip of the old giant branch. A provisional distance estimate for Pegasus of 1.7 Mpc is derived, placing it at the outer margins of the Local Group.

Hoessel, J. G.↗
NASA NTRS1991

Relative abundances in the low-metallicity dwarf irregular galaxy UGC 4483

UGC 4483 is a dwarf irregular galaxy in the M 81 group. Narrow-band optical imaging has revealed an H II region in UGC 4483 with an H-alpha flux of about 2 x 10 to the -13th erg/sq cm per A per s. Optical, UV and NIR spectroscopy of this H II region yield He, C, N, O, Ne, and S abundances for the ISM in this galaxy. With an oxygen abundance of 0.000021 12 + log(O/H) = 7.3, this galaxy is among the most metal-poor dwarf irregulars known to date. A comparison of the S/O abundance ratio in this galaxy with that in I Zw 18 supports the claim by Garnett (1990) that the S/O ratio is consistent with the solar ratio for low-metallicity dwarf irregulars. The C/O ratio in UGC 4483 is lower than that derived for I Zw 18 and, therefore, more in line with the trend seen in higher metallicity H II regions. The derived helium abundance is He/H = 0.075, which converts to a He mass fraction of 0.23, consistent with earlier determinations of the primordial He abundance.

Skillman, Evan D.↗
DOE OSTI2021

Prospects for measuring dark matter microphysics with observations of dwarf spheroidal galaxies

Dark matter annihilation in dwarf spheroidal (dSph) galaxies near the Milky Way has the potential to produce a detectable signature in gamma-rays. The amplitude of this signal depends on the dark matter density in a dSph, the dark matter particle mass, the number of photons produced in an annihilation, and the possibly velocity-dependent dark matter annihilation cross section. We argue that if the amplitude of the annihilation signal from multiple dSphs can be measured, it is possible to determine the velocity-dependence of the annihilation cross section. However, we show that doing so will require improved constraints on the dSph density profiles, including control of possible sources of systematic uncertainty. Making reasonable assumptions about future improvements, we make forecasts for the ability of current and future experiments — including Fermi, CTA and AMEGO — to constrain the dark matter annihilation velocity dependence.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗