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Register a new userMidlife Crises in Dwarf Galaxies in the NGC 5353/4 Group
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This third paper in a series about the dwarf galaxy populations in groups within the Local Supercluster concerns the intermediate mass (2.1 x 10^13 solar) NGC 5353/4 Group with a core dominated by S0 systems and a periphery of mostly spiral systems. Dwarf galaxies are strongly concentrated toward the core. The mass to light ratio M/L_R=105 in solar units is a factor 3 lower than for the two groups studied earlier in the series. The properties of the group suggest it is much less dynamically evolved than those two groups of early type galaxies. By comparison, the NGC 5353/4 Group lacks superluminous systems but has a large fraction of intermediate luminosity galaxies; or equivalently, a luminosity function with a flatter faint end slope. The luminosity function for the NGC 5353/4 Group should steepen as the intermediate luminosity galaxies merge. Evidence for the ongoing collapse of the group is provided by the unusually large incidence of star formation activity in small galaxies with early morphological types. The pattern in the distribution of galaxies with activity suggests a succession of infall events. Residual gas in dwarfs that enter the group is used up in sputtering events. The resolution of midlife crises is exhaustion.
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We present a compilation of galaxies in the NGC 1023 Group, an accumulation of late-type galaxies at a distance of 10 Mpc. Members at high and intermediate luminosities were identified from their spectroscopic velocities. Members at low luminosities were identified from their morphologies on wide-field CCD images. The faint-end slope is in the range -1.27 < alpha < -1.12. There is evidence for two dwarf galaxy populations: one in the halo of NGC 1023 that is dominated by dwarf elliptical galaxies, and one in the infall region surrounding NGC 1023 that contains mainly dwarf irregular galaxies. Similar distinctive populations are observed in the Local Group.
The NGC 1407 Group stands out among nearby structures by its properties that suggest it is massive and evolved. It shares properties with entities that have been called fossil groups: the 1.4 magnitude differential between the dominant elliptical galaxy and the second brightest galaxy comes close to satisfying the definition that has been used to define the fossil class. There are few intermediate luminosity galaxies, but a large number of dwarfs in the group. We estimate there are 250 group members to the depth of our survey. The slope of the faint end of the luminosity function (reaching M_R = -12) is alpha = -1.35. Velocities for 35 galaxies demonstrate that this group with one dominant galaxy has a mass of 7 X 10^13 M_sun and M/L_R = 340. Two galaxies in close proximity to NGC 1407 have very large blueshifts. The most notable is the second brightest galaxy, NGC 1400, with a velocity of -1072 km/s with respect to the group mean. We report the detection of X-ray emission from this galaxy and from the group.
We present first results of a survey of the Leo I group at 10 Mpc for M_R < -10 dwarf galaxies. This is part of a larger program to measure the faint end of the galaxy luminosity function in nearby poor groups. Our method is optimized to find Local-Group-like dwarfs down to dwarf spheroidal surface brightnesses, but we also find very large LSB dwarfs in Leo I with no Local Group counterpart. A preliminary measurement of the luminosity function yields a slope consistent with that measured in the Local Group.
We have carried out a detailed modelling of the dust heating and emission in the nearby, starbursting dwarf galaxy NGC 4214. Due to its proximity and the great wealth of data from the UV to the millimeter range (from GALEX, HST, {it Spitzer}, Herschel, Planck and IRAM) it is possible to separately model the emission from HII regions and their associated photodissociation regions (PDRs) and the emission from diffuse dust. Furthermore, most model parameters can be directly determined from the data leaving very few free parameters. We can fit both the emission from HII+PDR regions and the diffuse emission in NGC 4214 with these models with normal dust properties and realistic parameters.
Context. Ultra-compact dwarfs (UCDs) are stellar systems displaying colours and metallicities between those of globular clusters (GCs) and early-type dwarf galaxies, as well as sizes of Reff <= 100 pc and luminosities in the range -13.5 < MV < -11 mag. Although their origin is still subject of debate, the most popular scenarios suggest that they are massive star clusters or the nuclei of tidally stripped dwarf galaxies. Aims. NGC 5044 is the central massive elliptical galaxy of the NGC 5044 group. Its GC/UCD system is completely unexplored. Methods. In Gemini+GMOS deep images of several fields around NGC 5044 and in spectroscopic multi-object data of one of these fields, we detected an unresolved source with g~20.6 mag, compatible with being an UCD. Its radial velocity was obtained with FXCOR and the penalized pixel-fitting (pPXF) code. To study its stellar population content, we measured the Lick/IDS indices and compared them with predictions of single stellar population models, and we used the full spectral fitting technique. Results. The spectroscopic analysis of the UCD revealed a radial velocity that agrees with the velocity of the elliptical galaxy NGC 5044. From the Lick/IDS indices, we have obtained a luminosity-weighted age and metallicity of 11.7+/-1.4 Gyr and [Z/H] = -0.79 +/- 0.04 dex, respectively, as well as [alpha/Fe] = 0.30 +/- 0.06. From the full spectral fitting technique, we measured a lower age (8.52 Gyr) and a similar total metallicity ([Z/H] = -0.86 dex). Conclusions. Our results indicate that NGC 5044-UCD1 is most likely an extreme GC (MV ~ -12.5 mag) belonging to the GC system of the elliptical galaxy NGC 5044.
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