Stellar Populations in Bulges

We present line strengths in the bulges and inner disks of 38 galaxies in the local universe, including several galaxies whose bulges were previously identified as being disk-like in their colors or kinematics, to see if their spectral properties reveal evidence for secular evolution. We find that red bulges of all Hubble types are similar to luminous ellipticals in their central stellar populations. They have large luminosity-weighted ages, metallicities, and alpha/Fe ratios. Blue bulges can be separated into a metal-poor class that is restricted to late-types with small velocity dispersion and a young, metal-rich class that includes all Hubble types and velocity dispersions. Luminosity-weighted metallicities and alpha/Fe ratios are sensitive to central velocity dispersion and maximum disk rotational velocity. Red bulges and ellipticals follow the same scaling relations. We see differences in some scaling relations between blue and red bulges and between bulges of barred and unbarred galaxies. Most bulges have decreasing metallicity with increasing radius; galaxies with larger central metallicities have steeper gradients. Where positive age gradients (with the central regions being younger) are present, they are invariably in barred galaxies. The metallicities of bulges are correlated with those of their disks. While this and the differences between barred and unbarred galaxies suggest that secular evolution cannot be ignored, our results are generally consistent with the hypothesis that mergers have been the dominant mechanism responsible for bulge formation.Comment: 30 pages, 21 figures; submitted to MNRA

CRIMINAL ADVISORY JURIES: A SENSIBLE COMPROMISE FOR JURY SENTENCING ADVOCATES

Supreme Court Justice Neil Gorsuch recently noted that “juries in our constitutional order exercise supervisory authority over the judicial function by limiting the judge’s power to punish.” Yet in the majority of jurisdictions, contemporary judge-only sentencing practices neuter juries of their supervisory authority by divorcing punishment from guilt decisions. Moreover, without a chance to voice public disapproval at sentencing, juries are muted in their ability to express tailored, moral condemnation for distinct criminal acts. Although the modern aversion to jury sentencing is neither historically nor empirically justified, jury sentencing opponents are rightly cautious of abdicating sentencing power to laypeople. Nevertheless, jury endorsement of criminal sentencing is critical to the legitimacy of criminal law. It is also necessary if criminal law is to remain responsive to evolving social mores. Unfortunately, today, studies suggest that actual criminal sentences are largely detached, if not divergent, from community preference. The criminal advisory jury is a mechanism to solve these issues by allowing juries to express community sentiment on punishment while preserving the values inherent in autonomous judicial sentencing. The jury is one of the most democratic institutions within the United States and sits readily assembled for most criminal trials. Failing to solicit its views of just desert for the criminal it has convicted is an opportunity wasted; an opportunity the criminal advisory jury construct will seize

Morphology of the Nuclear Disk in M87

A deep, fuly sampled diffraction limited (FWHM ~ 70 mas) narrow-band image of the central region in M87 was obtained with the Wide Filed and Planetary Camera 2 of the Hubble Space Telescope using the dithering technique. The H-alpha+[NII] continuum subtracted image reveals a wealth of details in the gaseous disk structure described earlier by Ford et al. (1994). The disk morphology is dominated by a well defined three-arm spiral pattern. In addition, the major spiral arms contain a large number of small "arclets" covering a range of sizes (0.1-0.3 arcsec = 10-30 pc). The overall surface brightness profile inside a radius ~1.5" (100 pc) is well represented by a power-law I(mu) ~ mu^(-1.75), but when the central ~40 pc are excluded it can be equally well fit by an exponential disk. The major axis position angle remains constant at about PA_disk ~ 6 deg for the innermost ~1", implying the disk is oriented nearly perpendicular to the synchrotron jet (PA_jet ~ 291 deg). At larger radial distances the isophotes twist, reflecting the gas distribution in the filaments connecting to the disk outskirts. The ellipticity within the same radial range is e = 0.2-0.4, which implies an inclination angle of i~35 deg. The sense of rotation combined with the dust obscuration pattern indicate that the spiral arms are trailing.Comment: 5 pages, 3 postscript figures, to appear in the Proceedings of the M87 Workshop, Ringberg castle, Germany, 15-19 Sep 1997, also available from http://jhufos.pha.jhu.edu/~zlatan/papers.htm

Metallicity Distribution Functions of Four Local Group dwarf galaxies

We present stellar metallicities in Leo I, Leo II, IC 1613, and Phoenix dwarf galaxies derived from medium (F390M) and broad (F555W, F814W) band photometry using the Wide Field Camera 3 (WFC3) instrument aboard the Hubble Space Telescope. We measured metallicity distribution functions (MDFs) in two ways, 1) matching stars to isochrones in color-color diagrams, and 2) solving for the best linear combination of synthetic populations to match the observed color-color diagram. The synthetic technique reduces the effect of photometric scatter, and produces MDFs 30-50 % narrower than the MDFs produced from individually matched stars. We fit the synthetic and individual MDFs to analytical chemical evolution models (CEM) to quantify the enrichment and the effect of gas flows within the galaxies. Additionally, we measure stellar metallicity gradients in Leo I and II. For IC 1613 and Phoenix our data do not have the radial extent to confirm a metallicity gradient for either galaxy. We find the MDF of Leo I (dwarf spheroidal) to be very peaked with a steep metal rich cutoff and an extended metal poor tail, while Leo II (dwarf spheroidal), Phoenix (dwarf transition) and IC 1613 (dwarf irregular) have wider, less peaked MDFs than Leo I. A simple CEM is not the best fit for any of our galaxies, therefore we also fit the `Best Accretion Model' of Lynden-Bell 1975. For Leo II, IC 1613 and Phoenix we find similar accretion parameters for the CEM, even though they all have different effective yields, masses, star formation histories and morphologies. We suggest that the dynamical history of a galaxy is reflected in the MDF, where broad MDFs are seen in galaxies that have chemically evolved in relative isolation and narrowly peaked MDFs are seen in galaxies that have experienced more complicated dynamical interactions concurrent with their chemical evolution.Comment: 15 pages, 8 figures, accepted in A

Using Astrometry to Deblend Microlensing Events

We discuss the prospect of deblending microlensing events by observing astrometric shifts of the lensed stars. Since microlensing searches are generally performed in very crowded fields, it is expected that stars will be confusion limited rather than limited by photon statistics. By performing simulations of events in crowded fields, we find that if we assume a dark lens and that the lensed star obeys a power law luminosity function, $n(L)\propto L^{-\beta}$, over half the simulated events show a measurable astrometric shift. Our simulations included 20000 stars in a $256\times 256$ Nyquist sampled CCD frame. For $\beta=2$, we found that 58% of the events were significantly blended $(F_{\ast}/F_{tot}\leq 0.9)$, and of those, 73% had a large astrometric shift $(\geq 0.5 pixels)$. Likewise, for $\beta=3$, we found that 85% of the events were significantly blended, and that 85% of those had large shifts. Moreover, the shift is weakly correlated to the degree of blending, suggesting that it may be possible not only to detect the existence of a blend, but also to deblend events statistically using shift information.Comment: 24 pages, 7 postscript Figure

Imaging of the Merging Galaxy NGC 3597 and its Population of Proto--Globular Clusters

We present wide field-of-view near-infrared imaging from the NTT and very deep optical imaging from the HST of the young merging galaxy NGC 3597. The morphology of the galaxy and the properties of the newly formed proto-globular clusters (PGCs) are examined. Our K band data reveals the presence of a second nucleus, which provides further evidence that NGC 3597 is the result of a recent merger. Combining new K band photometry with optical photometry, we are able for the first time to derive a unique age for the newly formed PGCs of a few Myrs. This is consistent with the galaxy starburst age of < 10 Myrs. From deep HST imaging, we are able to probe the luminosity function ~8 magnitudes fainter than normal, old globular clusters, and confirm that the PGCs have a power-law distribution with a slope of ~-2.Comment: 19 pages, Latex, 10 figures, 4 tables, accepted by MNRA

Discovery of Multi-Phase Cold Accretion in a Massive Galaxy at z=0.7

We present detailed photo+collisional ionization models and kinematic models of the multi-phase absorbing gas, detected within the HST/COS, HST/STIS, and Keck/HIRES spectra of the background quasar TON 153, at 104 kpc along the projected minor axis of a star-forming spiral galaxy (z=0.6610). Complementary g'r'i'Ks photometry and stellar population models indicate that the host galaxy is dominated by a 4 Gyr stellar population with slightly greater than solar metallicity and has an estimated log(M*)=11 and a log(Mvir)=13. Photoionization models of the low ionization absorption, (MgI, SiII, MgII and CIII) which trace the bulk of the hydrogen, constrain the multi-component gas to be cold (logT=3.8-5.2) and metal poor (-1.68<[X/H]<-1.64). A lagging halo model reproduces the low ionization absorption kinematics, suggesting gas coupled to the disk angular momentum, consistent with cold accretion mode material in simulations. The CIV and OVI absorption is best modeled in a separate collisionally ionized metal-poor (-2.50<[X/H]<-1.93) warm phase with logT=5.3. Although their kinematics are consistent with a wind model, given the 2-2.5dex difference between the galaxy stellar metallicity and the absorption metallicity indicates the gas cannot arise from galactic winds. We discuss and conclude that although the quasar sight-line passes along the galaxy minor axis at projected distance of 0.3 virial radii, well inside its virial shock radius, the combination of the relative kinematics, temperatures, and relative metallicities indicated that the multi-phase absorbing gas arises from cold accretion around this massive galaxy. Our results appear to contradict recent interpretations that absorption probing the projected minor axis of a galaxy is sampling winds.Comment: 16 pages, 11 figures, accepted for publication in MNRA