34 research outputs found
On the Nature of the NGC 1275 System
Sub-arcsecond images, taken in B, R, and H-Alpha filters, and area
spectroscopy obtained with the WIYN 3.5-m telescope provide the basis for an
investigation of the unusual structures in the stellar body and ionized gas in
and around the Perseus cluster central galaxy, NGC 1275. Our H-Alpha filter is
tuned to gas at the velocity of NGC 1275, revealing complex, probably
unresolved, small-scale features in the extended ionized gas, located up to
50/h kpc from NGC 1275. The mean H-Alpha surface brightness varies little along
the outer filaments; this, together with the complex excitation state
demonstrated by spectra, imply that the filaments are likely to be tubes, or
ribbons, of gas. The morphology, location and inferred physical parameters of
the gas in the filaments are consistent with a model whereby the filaments form
through compression of the intracluster gas by relativistic plasma emitted from
the active nucleus of NGC 1275. Imaging spectroscopy with the Densepak fiber
array on WIYN suggests partial rotational support of the inner component of low
velocity ionized gas. We confirm and extend evidence for features in the
stellar body of NGC 1275, and identify outer stellar regions containing very
blue, probably very young, star clusters. We interpret these as evidence for
recent accretion of a gas-rich system, with subsequent star formation. We
suggest that two main processes, which may be causally connected, are
responsible for the rich phenomenology of the NGC 1275 system -- NGC 1275
experienced a recent merger/interaction with a group of gas-rich galaxies, and
recent outflows from its AGN have compressed the intracluster gas, and perhaps
the gas in the infalling galaxies, to produce a complex web of filaments.
(Abridged)Comment: AJ, accepted; a recommended full resolution version is available at
http://www.astro.wisc.edu/~chris/pera.p
Hubble Space Telescope survey of the Perseus Cluster -IV: Compact stellar systems in the Perseus Cluster core and Ultra Compact Dwarf formation in star forming filaments
We present the results of the first search for Ultra Compact Dwarfs (UCDs) in
the Perseus Cluster core, including the region of the cluster around the
unusual Brightest Cluster Galaxy (BCG) NGC 1275. Utilising Hubble Space
Telescope Advanced Camera for Surveys imaging, we identify a sample of 84 UCD
candidates with half-light radii 10 pc < r_e < 57 pc out to a distance of 250
kpc from the cluster centre, covering a total survey area of ~70 armin^2. All
UCDs in Perseus lie in the same size-luminosity locus seen for confirmed UCDs
in other regions of the local Universe. The majority of UCDs are brighter than
M_R = -10.5, and lie on an extrapolation of the red sequence followed by the
Perseus Cluster dwarf elliptical population to fainter magnitudes. However,
three UCD candidates in the vicinity of NGC 1275 are very blue, with colours
(B-R)_0 < 0.6 implying a cessation of star formation within the past 100 Myr.
Furthermore, large blue star clusters embedded in the star forming filaments
are highly indicative that both proto-globular clusters (GCs) and proto-UCDs
are actively forming at the present day in Perseus. We therefore suggest star
forming filaments as a formation site for some UCDs, with searches necessary in
other low redshift analogues of NGC 1275 necessary to test this hypothesis. We
also suggest that tidal disruption of dwarf galaxies is another formation
channel for UCD formation in the core of Perseus as tidal disruption is ongoing
in this region as evidenced by shells around NGC 1275. Finally, UCDs may simply
be massive GCs based on strong similarities in the colour trends of the two
populations.Comment: 18 pages, 20 figures, 3 tables. Accepted for publication in MNRA
EDM constraints on flavored CP-violating phases
The CP-violating phenomenology of the MSSM with Minimal Flavor Violation
(MFV) in the lepton sector is revisited. To this end, the most general
parametrizations of the slepton soft-breaking terms are constructed assuming a
seesaw mechanism of type I. After a critical reassessment of how the
CP-symmetry is broken within the MFV framework, all possible CP-violating
phases are introduced. From the strong hierarchy of their contributions to the
Electric Dipole Moments (EDMs), these phases are split into three classes:
flavor-blind, flavor-diagonal and flavor off-diagonal. In particular, the
phases from the neutrino sector belong to the last class; they start to
contribute only at the second order in the mass-insertion approximation and
have thus a negligible effect. It is then shown that to each class of phases
corresponds a unique largely dominant term in the MFV expansion. Numerically,
for a realistic range of MSSM and neutrino parameters, such that B(mu --> e
gamma) does not exceed its experimental bound, the three types of phases are
found to be allowed by the current bound on the electron EDM, though the next
generation of experiments should constrain tightly the flavor-blind phase.
Finally, we relax the MFV hypothesis and show how in the general MSSM, the MFV
operator basis can be used to judge of the naturality of the slepton
soft-breaking terms.Comment: Latex, 24 pages, 2 figures. Minor changes; one reference added. To
appear in Nucl. Phys.
A Description of Quasar Variability Measured Using Repeated SDSS and POSS Imaging
We provide a quantitative description and statistical interpretation of the
optical continuum variability of quasars. The Sloan Digital Sky Survey (SDSS)
has obtained repeated imaging in five UV-to-IR photometric bands for 33,881
spectroscopically confirmed quasars. About 10,000 quasars have an average of 60
observations in each band obtained over a decade along Stripe 82 (S82), whereas
the remaining ~25,000 have 2-3 observations due to scan overlaps. The observed
time lags span the range from a day to almost 10 years, and constrain quasar
variability at rest-frame time lags of up to 4 years, and at rest-frame
wavelengths from 1000A to 6000A. We publicly release a user-friendly catalog of
quasars from the SDSS Data Release 7 that have been observed at least twice in
SDSS or once in both SDSS and the Palomar Observatory Sky Survey, and we use it
to analyze the ensemble properties of quasar variability. Based on a damped
random walk (DRW) model defined by a characteristic time scale and an
asymptotic variability amplitude that scale with the luminosity, black hole
mass, and rest wavelength for individual quasars calibrated in S82, we can
fully explain the ensemble variability statistics of the non-S82 quasars such
as the exponential distribution of large magnitude changes. All available data
are consistent with the DRW model as a viable description of the optical
continuum variability of quasars on time scales of ~5-2000 days in the rest
frame. We use these models to predict the incidence of quasar contamination in
transient surveys such as those from PTF and LSST.Comment: 33 pages, 19 figures, replaced with accepted version. Catalog is
available at http://www.astro.washington.edu/users/ivezic/macleod/qso_dr7
The study of Jyotiḥśāstra and the uses of philosophy of science
This is one of a group of essays (collected in this issue of the journal) about methodological considerations that have arisen for the project on the "Sanskrit knowledge systems on the eve of colonialis." For the history of the exact sciences in Sanskrit, or Jyotiḥśāstra, in the early modern period, there are special problems. These have to do with the historically anomalous status of the exact sciences among the śāstras or Sanskrit knowledge systems, and with the predominantly "internalist" method by which most recent research on Jyotiḥśāstra has been carried out. The essay considers the usefulness for tackling these problems of recent writing elsewhere in the history and philosophy of science, especially the work of Hacking
Ends of the Mahābhārata
The assertion that the Mahābhārata (MBh) narrative is innately incapable of achieving a conclusion has attained the status of a disciplinary truism in the epic’s study. My thesis challenges this prevalent assumption by proposing an un-investigated path of inquiry into the philological, historical, literary and semantic aspects of the epic. The thesis discusses the ending of the MBh, the Svargārohaṇa parvan (SĀ) by exploring several trajectories: the study of the SĀ in epic scholarship; its reception in the later tradition in Sanskrit literature; and finally, the problematic aspects of the SĀ and its relation to the rest of the narrative. It first points out that in comparison to other MBh episodes, the SĀ has been received with significant disregard or suppression in the literature commenting on the epic. Second, it characterizes the nature of the suppression of the SĀ in each of the three literary strands commenting on the MBh (epic scholarship, Sanskrit adaptations and theoretical discourses). It argues that all of these considerations, which are external to the MBh, have tended, in various modes, to suppress, ignore or overlook the importance of the SĀ. The thesis then proceeds to argue that on the most significant and internal level of the text itself, the SĀ is intrinsically consistent with the rest of the MBh narrative, and that this makes it thematically integral to the text as a whole. This argument derives from the importance with which this study addresses the moment of the condemnation of dharma in the SĀ, and is furthered by a philological and semantic study, as well as textual analyses of the multiple occurrences of the Sanskrit verb garh throughout the MBh. The use of this verb by the epic protagonist, Yudhiṣṭhira, in condemning his father, Dharma, at the last scenes of the SĀ comprises a key moment that bears significant and myriad implications upon the understanding of this pivotal concept (dharma), to which the entire epic is devoted.EThOS - Electronic Theses Online ServiceGBUnited Kingdo