400 research outputs found
The Magellanic Squall: Gas Replenishment from the Small to Large Magellanic Cloud
We first show that a large amount of metal-poor gas is stripped from the
Small Magellanic Cloud (SMC) and fallen into the Large Magellanic Cloud (LMC)
during the tidal interaction between the SMC, the LMC, and the Galaxy over the
last 2 Gyrs. We propose that this metal-poor gas can closely be associated with
the origin of LMC's young and intermediate-age stars and star clusters with
distinctively low-metallicities with [Fe/H] < -0.6. We numerically investigate
whether gas initially in the outer part of the SMC's gas disk can be stripped
during the LMC-SMC-Galaxy interaction and consequently can pass through the
central region (R<7.5 kpc) of the LMC. We find that about 0.7 % and 18 % of the
SMC's gas can pass through the central region of the LMC about 1.3 Gyr ago and
0.2 Gyr ago, respectively. The possible mean metallicity of the replenished gas
from the SMC to LMC is about [Fe/H] = -0.9 to -1.0 for the two interacting
phases. These results imply that the LMC can temporarily replenish gas supplies
through the sporadic accretion and infall of metal-poor gas from the SMC. These
furthermore imply that if these gas from the SMC can collide with gas in the
LMC to form new stars in the LMC, the metallicities of the stars can be
significantly lower than those of stars formed from gas initially within the
LMC.Comment: 5 pages, 5 figures, accepted in MNRAS Letter
Dynamical Effects of CDM Subhalos on a Galactic Disk
We investigate the dynamical interaction between a galactic disk and
surrounding numerous dark subhalos as expected for a galaxy-sized halo in the
cold dark matter (CDM) models. Our particular interest is to what extent
accretion events of subhalos into a disk are allowed in light of the observed
thinness of a disk. Several models of subhalos are considered in terms of their
internal density distribution, mass function, and spatial and velocity
distributions. Based on a series of N-body simulations, we find that the disk
thickening quantified by the change of its scale height, Delta z_d, depends
strongly on the individual mass of an interacting subhalo M_{sub}. This is
described by the relation, Delta z_d / R_d = 8 Sum_{j=1}^N (M_{sub,j}/M_d)**2,
where R_d is a disk scale length, M_d is a disk mass, and N is the total number
of accretion events of subhalos inside a disk region (< 3R_d). Using this
relation, we find that an observed thin disk has not ever interacted with
subhalos with the total mass of more than 15% disk mass. Also, a less massive
disk with smaller circular velocity V_c is more affected by subhalos than a
disk with larger V_c, in agreement with the observation. Further implications
of our results for the origin of a thick disk component are also discussed.Comment: 12 pages, 9 figures, accepted by PAS
A Technique Fof Determining the Extragalactic Distance Scale
We propose a method of distance determination based on the internal structure
and dynamics of disk galaxies. The method relies on the universal luminosity
profile of a stellar disk represented by an exponential law. Calibrating nearby
galaxies with known distances, it is found that the scale length of the disk is
tightly correlated with the specific combination of central surface brightness
{\it and} rotational velocity at a characteristic radius of 2.15 scale lengths
from the center. This suggests that the scale length of the disk may be used as
an indicator for extragalactic distance scale. The application of this relation
to M51 and M100 allows us to arrive at the distances of about 6 Mpc and 14 Mpc,
respectively, implying a Hubble constant of km s
Mpc.Comment: 12pp + 2 figures, included as uuencoded postscript file, to appear in
ApJ (Part1), TH94092
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