1,374 research outputs found
Gas Mass Fractions and Star Formation in Blue-Sequence E/S0 Galaxies
Recent work has identified a population of low-redshift E/S0 galaxies that
lie on the blue sequence in color vs. stellar mass parameter space, where
spiral galaxies typically reside. While high-mass blue-sequence E/S0s often
resemble young merger or interaction remnants likely to fade to the red
sequence, we focus on blue-sequence E/S0s with lower stellar masses (< a few
10^10 M_sun), which are characterized by fairly regular morphologies and
low-density field environments where fresh gas infall is possible. This
population may provide an evolutionary link between early-type galaxies and
spirals through disk regrowth. Focusing on atomic gas reservoirs, we present
new GBT HI data for 27 E/S0s on both sequences as well as a complete tabulation
of archival HI data for other galaxies in the Nearby Field Galaxy Survey.
Normalized to stellar mass, the atomic gas masses for 12 of the 14
blue-sequence E/S0s range from 0.1 to >1.0. These gas-to-stellar mass ratios
are comparable to those of spiral and irregular galaxies and have a similar
dependence on stellar mass. Assuming that the HI is accessible for star
formation, we find that many of our blue-sequence E/S0s can increase in stellar
mass by 10-60% in 3 Gyr in both of two limiting scenarios, exponentially
declining star formation and constant star formation. In a constant star
formation scenario, about half of the blue-sequence E/S0s require fresh gas
infall on a timescale of <3 Gyr to avoid exhausting their atomic gas reservoirs
and evolving to the red sequence. We present evidence that star formation in
these galaxies is bursty and likely involves externally triggered gas inflows.
Our analysis suggests that most blue-sequence E/S0s are indeed capable of
substantial stellar disk growth on relatively short timescales. (abridged)Comment: ApJ, accepted, 26 pages with 12 figures (5 color), 5 table
Building a CCD Spectrograph for Educational or Amateur Astronomy
We discuss the design of an inexpensive, high-throughput CCD spectrograph for
a small telescope. By using optical fibers to carry the light from the
telescope focus to a table-top spectrograph, one can minimize the weight
carried by the telescope and simplify the spectrograph design. We recently
employed this approach in the construction of IntroSpec, an instrument built
for the 16-inch Knowles Telescope on the Harvard College campus.Comment: 17 pages including 7 figures, PASP, accepted (higher resolution
figures at http://cfa-www.harvard.edu/~sheila/introspec.ps.gz
The Ubiquity and Dual Nature of Ultra Compact Dwarfs
We present the discovery of several Ultra Compact Dwarfs (UCDs) located in
field/group environments. Examination of these objects, plus literature
objects, confirms the existence of two distinct formation channels for UCDs. We
find that the UCDs we have discovered around the group elliptical NGC3923 (and
UCDs generally) have properties consistent with their being the most luminous
members of the host galaxy's globular cluster (GC) system. We describe UCDs of
this type as giant GCs (GGCs). In contrast, the UCD we have found associated
with the isolated S0 NGC4546 is clearly the result of the stripping of a
nucleated companion galaxy. The young age (~3.4 Gyr) of the UCD, the lack of a
correspondingly young GC population, the apparently short dynamical friction
decay timescale (~0.5 Gyr) of the UCD, and the presence of a counterrotating
gas disc in the host galaxy (co-rotating with the UCD) together suggest that
this UCD is the liberated nucleus remaining after the recent stripping of a
companion by NGC4546. We suggest a general scheme that unifies the formation of
GCs, UCDs, and galaxy nuclei. In this picture "normal" GCs are a composite
population, composed of GCs formed in situ, GCs acquired from accreted
galaxies, and a population of lower mass stripped dwarf nuclei masquerading as
GCs. Above a "scaling onset mass" of 2x10^6 Msun (Mv ~ -10), UCDs emerge
together with a mass-size relation and a likely mass-metallicity relation (the
"blue tilt"). In the mass range up to 7x10^7 Msun (Mv ~ -13) UCDs comprise a
composite population of GGCs and stripped nuclei. Above 7x10^7 Msun, UCDs must
be almost exclusively stripped nuclei, as no sufficiently rich GC systems exist
to populate such an extreme of the GCLF.Comment: 23 pages, 16 figures, accepted for publication in MNRA
UCDs as Probes of the Major and Minor Merger Histories of Galaxies
Two competing theories posit that Ultra Compact Dwarfs (UCDs) form either as
the stripped nuclei of dwarf galaxies or as giant globular clusters (GGCs)
associated with the largest globular cluster (GC) systems. By focussing on the
field and group environments where young UCDs may be most common, we have
discovered the first UCD that is clearly the result of recent (<4 Gyr ago)
stripping of a companion galaxy. However, we have also found a definitive case
of a multiple-UCD system created via GC formation processes, which are likely
associated with major galaxy mergers. We demonstrate that it is possible to
reliably distinguish the two types of UCD, thereby probing both the major and
minor merger histories of individual galaxies.Comment: 2 pages, 1 figure, to appear in the proceedings of the conference "A
Universe of Dwarf Galaxies" (Lyon, June 14-18, 2010
E/S0 Galaxies on the Blue Color-Stellar Mass Sequence at z=0: Fading Mergers or Future Spirals?
We identify a population of morphologically defined E/S0 galaxies lying on
the blue sequence at the present epoch. Using three samples, we analyze
blue-sequence E/S0s with stellar masses >10^8 Msun, arguing that individual
objects may be evolving either up toward the red sequence or down into the blue
sequence. Blue-sequence E/S0 galaxies become more common with decreasing
stellar mass, comprising <2% of E/S0s near the "shutdown mass" M_s ~ 1-2 x
10^11 Msun, increasing to >5% near the "bimodality mass" M_b ~ 3 x 10^10 Msun,
and sharply rising to >20-30% below the "threshold mass" M_t ~ 4-6 x 10^9 Msun.
The strong emergence of blue-sequence E/S0s below M_t coincides with a
previously reported global increase in mean atomic gas fractions below M_t for
galaxies of all types on both sequences, suggesting that the availability of
cold gas may be basic to blue-sequence E/S0s' existence. Environmental analysis
reveals that many sub-M_b blue-sequence E/S0s reside in low to intermediate
density environments. In mass-radius and mass-sigma scaling relations,
blue-sequence E/S0s are more similar to red-sequence E/S0s than to late-type
galaxies, but they represent a transitional class. While some of them,
especially in the high-mass range from M_b to M_s, resemble major-merger
remnants that will likely fade onto the red sequence, most blue-sequence E/S0s
below M_b show signs of disk and/or pseudobulge building, which may be enhanced
by companion interactions. We argue that sub-M_b blue-sequence E/S0s occupy a
"sweet spot" in stellar mass and concentration, with both abundant gas and
optimally efficient star formation, which may enable the formation of large
spiral disks. [abridged]Comment: AJ, submitted, revised, 21 pages with 15 figures (one in two parts,
one color); full resolution version available at
http://www.physics.unc.edu/~sheila/kgb.pd
The Relationship Between Molecular Gas and Star Formation in Low-Mass E/S0 Galaxies
We consider the relationship between molecular-gas and star-formation surface
densities in 19 morphologically defined E/S0s with stellar mass <~ 4x10^10
M_sun, paying particular attention to those found on the blue sequence in color
vs. stellar mass parameter space, where spiral galaxies typically reside. While
some blue-sequence E/S0s must be young major-merger remnants, many low-mass
blue-sequence E/S0s appear much less disturbed, and may be experiencing the
milder starbursts associated with inner-disk building as spirals (re)grow. For
a sample of eight E/S0s (four blue-, two mid-, and two red-sequence) whose
CARMA CO(1-0), Spitzer MIPS 24um, and GALEX FUV emission distributions are
spatially resolved on a 750pc scale, we find roughly linear relationships
between molecular-gas and star-formation surface densities within all galaxies,
with power law indices N = 0.6-1.9 (median 1.2). Adding 11 more blue-sequence
E/S0s whose CO(1-0) emission is not as well resolved, we find that most of our
E/S0s have global 1-8 kpc aperture-averaged molecular-gas surface densities
overlapping the range spanned by the disks and centers of spiral galaxies.
While many of our E/S0s fall on the same Schmidt-Kennicutt relation as local
spirals, ~80% (predominantly on the blue sequence) are offset towards
apparently higher molecular-gas star formation efficiency (i.e., shorter
molecular gas depletion time). Possible interpretations of the elevated
efficiencies include bursty star formation similar to that in local dwarf
galaxies, H2 depletion in advanced starbursts, or simply a failure of the
CO(1-0) emission to trace all of the molecular gas.Comment: ApJL, accepted, 16 pages with 3 color figures, 2 table
Efficacy of lactic acid bacteria in the reduction of trimethylamine-nitrogen and related spoilage derivatives of fresh Indian mackerel fish chunks
Different strains of lactic acid bacteria (LAB) such as Pediococcus acidilactici, Pediococcus pentosaceous, Streptococcus thermophilus, Lactococcus lactis, Lactobacillus plantarum, Lactobacillus acidophilus and Lactobacillus helveticus were procured from the NCL (National Chemical Laboratory), Pune, India. These LAB cells were individually coated on the dressed fresh mackerel fish chunks and incubated at 37°C for two days. Different quality indices such as trimethylamine nitrogen (TMA-N), total volatile basic nitrogen (TVB-N), peroxide value (PV) and free fatty acids (FFA) were estimated for 2 days period. P. acidilactici cell coat reduced 40 mg% of TMA-N, 47.66 mg% of FFA, 97 mg% of PV and 97 mg% of PV when compared with control. The TMA-N content was reduced to 20 mg% by S. thermophilus cell coat on the treated fish when compared with control, while no reduction was observed on TVB-N. Out of the seven LAB tested for TMA-N reduction, Lb. helveticus and Lc. lactis reduced 150 mg% identically. All the LAB grew in increasing and decreasing trends using available carbohydrate present in the fish. For, FFA reduction, Lb. plantarum showed the highest (188%) as compared to P. pentosaceous and P. acidilactici followed by S. thermophilus. P. pentasaceous and P. acidilactici showed the highest PV reduction as 98 and 83 milli equivalent fat/kg of fats, when compared with Lb. plantarum in the control. Out of seven LAB tested for quality indices reduction, Lb. helveticus, Lc. lactis and P. acidilactici were the best LAB to control TMA-N and TVB-N, respectively. Lb. acidophilus, showed the best in the reduction of FFA. Therefore, this study confirms that LAB can be used to preserve freshfish through controlling spoilage bacteria and amines for a short period of time. Inplace of chemical preservatives, LAB may be use to extend the shelf life of fish.Keywords: Lactic acid bacteria, reduction of spoilage indices, trimethylamine nitrogen (TMA-N), total volatile basic nitrogen (TVB-N), peroxide value (PV), free fatty acids (FFA), mackerel chunk
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