PROBING THE CORES OF DENSE GLOBULAR CLUSTERS WITH THE HUBBLE SPACE TELESCOPE

GUHATHAKURTA PURAGRA The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1

THE LUMINOSITY-LINEWIDTH RELATION AS A PROBE OF THE EVOLUTION OF FIELD GALAXIES

GUHATHAKURTA PURAGRA,ING KRISTINE,RIX HANS-WALTER,COLLESS MATTHEW,WILLIAMS TED The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1

The nature of distant faint blue field galaxies remains a mystery, despite the fact that much attention has been devoted to this subject in the last decade. Galaxy counts, particularly those in the optical and near ultraviolet bandpasses, have been demonstrated to be well in excess of those expected in the 'no-evolution' scenario. This has usually been taken to imply that galaxies were brighter in the past, presumably due to a higher rate of star formation. More recently, redshift surveys of galaxies as faint as B$\~$24 have shown that the mean redshift of faint blue galaxies is lower than that predicted by standard evolutionary models (de-signed to fit the galaxy counts). The galaxy number count data and redshift data suggest that evolutionary effects are most prominent at the faint end of the galaxy luminosity function. While these data constrain the form of evolution of the overall luminosity function, they do not constrain evolution in individual galaxies. We are carrying out a series of observations as part of a long-term program aimed at a better understanding of the nature and amount of luminosity evolution in individual galaxies. Our study uses the luminosity-linewidth relation (Tully-Fisher relation) for disk galaxies as a tool to study luminosity evolution. Several studies of a related nature are being carried out by other groups. A specific experiment to test a 'no-evolution' hypothesis is presented here. We have used the AUTOFIB multifibre spectro-graph on the 4-metre Anglo-Australian Telescope (AAT) and the Rutgers Fabry-Perot imager on the Cerro Tolalo lnteramerican Observatory (CTIO) 4-metre tele-scope to measure the internal kinematics of a representative sample of faint blue field galaxies in the red-shift range z = 0.15-0.4. The emission line profiles of [OII] and [OIII] in a typical sample galaxy are significantly broader than the instrumental resolution (100-120 km $s^{-l}$), and it is possible to make a reliable de-termination of the linewidth. Detailed and realistic simulations based on the properties of nearby, low-luminosity spirals are used to convert the measured linewidth into an estimate of the characteristic rotation speed, making statistical corrections for the effects of inclination, non-uniform distribution of ionized gas, rotation curve shape, finite fibre aperture, etc.. The (corrected) mean characteristic rotation speed for our distant galaxy sample is compared to the mean rotation speed of local galaxies of comparable blue luminosity and colour. The typical galaxy in our distant sample has a B-band luminosity of about 0.25 L$\ast$ and a colour that corresponds to the Sb-Sd/Im range of Hub-ble types. Details of the AUTOFIB fibre spectroscopic study are described by Rix et al. (1996). Follow-up deep near infrared imaging with the 10-metre Keck tele-scope+ NIRC combination and high angular resolution imaging with the Hubble Space Telescope's WFPC2 are being used to determine the structural and orientation parameters of galaxies on an individual basis. This information is being combined with the spatially resolved CTIO Fabry-Perot data to study the internal kinematics of distant galaxies (Ing et al. 1996). The two main questions addressed by these (preliminary studies) are: 1. Do galaxies of a given luminosity and colour have the same characteristic rotation speed in the distant and local Universe? The distant galaxies in our AUTOFIB sample have a mean characteristic rotation speed of $\~$70 km $s^{-l}$ after correction for measurement bias (Fig. 1); this is inconsistent with the characteristic rotation speed of local galaxies of comparable photometric proper-ties (105 km $s^{-l}$) at the > $99\%$ significance level (Fig. 2). A straightforward explanation for this discrepancy is that faint blue galaxies were about 1-1.5 mag brighter (in the B band) at z $\~$ 0.25 than their present-day counterparts. 2. What i

Regulation of Αlpha-Synuclein Gene (SNCA) by Epigenetic Modifier TET1 in Parkinson Disease

Subhrangshu Guhathakurta,Min Kyung Song,Sambuddha Basu,Goun Je,Ana Clara Cristovao,Yoon-Seong Kim 대한배뇨장애요실금학회 2022 International Neurourology Journal Vol.26 No.S2

Purpose: Deregulation of SNCA encoding α-synuclein (α-SYN) has been associated with both the familial and sporadic forms of Parkinson disease (PD). Epigenetic regulation plays a crucial role in PD. The intron1 of SNCA harbors a large unmethylated CpG island. Ten-eleven translocation methylcytosine dioxygenase 1 (TET1), a CpG island binding protein, can repress gene expression by occupying hypomethylated CpG-rich promoters, and therefore SNCA could be a target for TET1. We investigated whether TET1 binds to SNCA-intron1 and regulates gene expression. Methods: The dopaminergic neuronal cell line, ReNcell VM, was used. Reverse transcription-polymerase chain reaction (RTPCR), real time-quantitative PCR, Western blot, dot-blot, and Chromatin immunoprecipitation were conducted. The substantia nigra tissues of postmortem PD samples were used to confirm the level of TET1 expression. Results: In the human dopaminergic cell line, ReNcell VM, overexpression of the DNA-binding domain of TET1 (TET1- CXXC) led to significant repression of α-SYN. On the contrary, knocking down of TET1 led to significantly higher expression of α-SYN. However, overexpression of the DNA-hydroxymethylating catalytic domain of TET1 failed to change the expression of α-SYN. Altogether, we showed that TET1 is a repressor for SNCA, and a CXXC domain of TET1 is the primary mediator for this repressive action independent of its hydroxymethylation activity. TET1 levels in PD patients are significantly lower than that in the controls. Conclusions: We identified that TET1 acts as a repressor for SNCA by binding the intron1 regions of the gene. As a high level of α-SYN is strongly implicated in the pathogenesis of PD, discovering a repressor for the gene encoding α-SYN is highly important for developing novel therapeutic strategies for the disease.

STELLAR KINEMATICS AND STRUCTURAL PROPERTIES OF VIRGO CLUSTER DWARF EARLY-TYPE GALAXIES FROM THE SMAKCED PROJECT. II. THE SURVEY AND A SYSTEMATIC ANALYSIS OF KINEMATIC ANOMALIES AND ASYMMETRIES

Toloba, E.,Guhathakurta, P.,Peletier, R. F.,Boselli, A.,Lisker, T.,Falcó,n-Barroso, J.,Simon, J. D.,van de Ven, G.,Paudel, S.,Emsellem, E.,Janz, J.,den Brok, M.,Gorgas, J.,Hensler, G.,Laurikaine IOP Publishing 2014 The Astrophysical journal Supplement series Vol.215 No.2

<P>We present spatially resolved kinematics and global stellar populations and mass-to-light ratios for a sample of 39 dwarf early-type (dE) galaxies in the Virgo cluster studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. This sample is representative of the early-type population in the Virgo cluster in the absolute magnitude range -19.0 < M-r < -16.0 and of all morphological subclasses found in this galaxy population. For each dE, we measure the rotation curve and velocity dispersion profile and fit an analytic function to the rotation curve. We study the significance of the departure of the rotation curve from the best-fit analytic function (poorly fit) and of the difference between the approaching and receding sides of the rotation curve (asymmetry). Our sample includes two dEs with kinematically decoupled cores that have been previously reported. We find that 62 +/- 8% (23 out of the 39) of the dEs have a significant anomaly in their rotation curve. Analysis of the images reveals photometric anomalies for most galaxies. However, there is no clear correlation between the significance of the photometric and kinematic anomalies. We measure age-sensitive (H-beta and H-gamma A) and metallicity sensitive (Fe4668 and Mgb) Lick spectral indices in the LIS-5 angstrom system. This population of galaxies exhibits a wide range of ages and metallicities; we also find that 4 dEs show clear evidence of emission partially filling in the Balmer absorption lines. Finally, we estimate the total masses and dark matter fractions of the dEs and plot them in the mass-size, themass-velocity dispersion, and the fundamental plane scaling relations. The dEs seem to be the bridge between massive early-type galaxies and dSphs, and have a median total mass within the R-e of logM(e) = 9.1 +/- 0.2 and a median dark matter fraction within the R-e of f(DM) = 46 +/- 18%. Any formation model for the dE galaxy class must account for this diversity of kinematic and photometric anomalies and stellar populations.</P>

NADPH Oxidase 1 Mediates α -Synucleinopathy in Parkinson's Disease

Cristovao, A.C.,Guhathakurta, S.,Bok, E.,Je, G.,Yoo, S.D.,Choi, D.-H.,Kim, Y.-S. Society for Neuroscience 2012 The Journal of neuroscience Vol.32 No.42

NADPH Oxidase 1-Mediated Oxidative Stress Leads to Dopamine Neuron Death in Parkinson's Disease

Choi, Dong-Hee,Cristó,vã,o, Ana Clara,Guhathakurta, Subhrangshu,Lee, Jongmin,Joh, Tong H.,Beal, M. Flint,Kim, Yoon-Seong Mary Ann Liebert 2012 ANTIOXIDANTS AND REDOX SIGNALING Vol.16 No.10

THE NEXT GENERATION VIRGO CLUSTER SURVEY. XXII. SHELL FEATURE EARLY-TYPE DWARF GALAXIES IN THE VIRGO CLUSTER

Paudel, Sanjaya,Smith, Rory,Duc, Pierre-Alain,Cô,té,, Patrick,Cuillandre, Jean-Charles,Ferrarese, Laura,Blakeslee, John P.,Boselli, Alessandro,Cantiello, Michele,Gwyn, S. D. J.,Guhathakurta American Astronomical Society 2017 The Astrophysical Journal Vol.834 No.1

<P>The Next Generation Virgo Cluster Survey is a deep (with a 2 sigma detection limit mu g = 29 mag arcsec(-2) in the g-band) optical panchromatic survey targeting the Virgo cluster from its core to virial radius, for a total areal coverage of 104 square degrees. As such, the survey is well suited for the study of galaxies' outskirts, haloes, and low surface brightness features that arise from dynamical interactions within the cluster environment. We report the discovery of extremely faint (mu g > 25 mag arcsec(-2)) shells in three Virgo cluster early-type dwarf galaxies: VCC. 1361, VCC. 1447, and VCC. 1668. Among them, VCC. 1447 has an absolute magnitude Mg = -11.71 mag and is the least massive galaxy with a shell system discovered to date. We present a detailed study of these low surface brightness features. We detect between three and four shells in each of our galaxies. Within the uncertainties, we find no evidence of a color difference between the galaxy main body and shell features. The observed arcs of the shells are located up to several effective radii of the galaxies. We further explore the origin of these low surface brightness features with the help of idealized numerical simulations. We find that a near equal mass merger is best able to reproduce the main properties of the shells, including their quite symmetric appearance and their alignment along the major axis of the galaxy. The simulations provide support for a formation scenario in which a recent merger, between two near-equal mass, gas-free dwarf galaxies, forms the observed shell systems.</P>