Spectroscopy of Globular Clusters in M81

We present moderate-resolution spectroscopy of globular clusters (GCs) around the Sa/Sb spiral galaxy M81 (NGC 3031). Sixteen candidate clusters were observed with the Low Resolution Imaging Spectrograph on the Keck I telescope. All are confirmed as bona fide GCs, although one of the clusters appears to have been undergoing a transient event during our observations. In general, the M81 globular cluster system (GCS) is found to be very similar to the Milky Way (MW) and M31 systems, both chemically and kinematically. A kinematic analysis of the velocities of 44 M81 GCS, (the 16 presented here and 28 from previous work) strongly suggests that the red, metal-rich clusters are rotating in the same sense as the gas in the disk of M81. The blue, metal-poor clusters have halo-like kinematics, showing no evidence for rotation. The kinematics of clusters whose projected galactocentric radii lie between 4 and 8 kpc suggest that they are rotating much more than those which lie outside these bounds. We suggest that these rotating, intermediate-distance clusters are analogous to the kinematic sub-population in the metal-rich, disk GCs observed in the MW and we present evidence for the existence of a similar sub-population in the metal-rich clusters of M31. With one exception, all of the M81 clusters in our sample have ages that are consistent with MW and M31 GCs. One cluster may be as young as a few Gyrs. The correlations between absorption-line indices established for MW and M31 GCs also hold in the M81 cluster system, at least at the upper end of the metallicity distribution (which our sample probes). On the whole, the mean metallicity of the M81 GCS is similar to the metallicity of the MW and M31 GCSs. The projected mass of M81 is similar to the masses of the MW and M31. Its mass profile indicates the presence of a dark matter halo.Comment: 35 pages, including 11 figures and 9 tables. Accepted for publication in the Astronomical Journa

The Chemical Properties of Milky Way and M31 Globular Clusters: I. A Comparative Study

A comparative analysis is performed between high-quality integrated spectra of 30 globular clusters in M31, 20 Milky Way clusters, and a sample of field and cluster elliptical galaxies. We find that the Lick CN indices in the M31 and Galactic clusters are enhanced relative to the bulges of the Milky Way, M31, and elliptical spheroids. Although not seen in the Lick CN indices, the near-UV cyanogen feature (3883 A) is strongly enhanced in M31 clustesr with respect to the Galactic globulars at metallicities, --1.5<[Fe/H]<--0.3. Carbon shows signs of varying amongst these two groups. For [Fe/H]>--0.8, we observe no siginificant differences in the Hdelta, Hgamma, or Hbeta indices between the M31 and Galactic globulars. The sample of ellipticals lies offset from the loci of all the globulars in the Cyanogen--[MgFe], and Balmer--[MgFe] planes. Six of the M31 cluster spectra appear young, and are projected onto the M31 disk. Population synthesis models suggest that these are metal-rich clusters with ages 100--800 Myr, metallicities --0.20 < [Fe/H] <0.35, and masses 0.7 -7.0x10^4 Msun. Two other young clusters are Hubble V in NGC 205, and an older (~3 Gyr) cluster ~7 kpc away from the plane of the disk. The six clusters projected onto the disk rotate in a similar fashion to the HI gas in M31, and three clusters exhibit thin disk kinematics (Morrison et al.). Dynamical masses and structural parameters are required for these objects to determine whether they are massive open clusters or globular clusters. If the latter, our findings suggest globular clusters may trace the build up of galaxy disks. In either case, we conclude that these clusters are part of a young, metal-rich disk cluster system in M31, possibly as young as 1 Gyr old.Comment: 52 pages, 14 figures, 8 tables, minor revisions in response to referee, conclusions remain the same. Scheduled to appear in the October 2004 issue of The Astronomical Journa

Globular clusters in the outer halo of M31: the survey

We report the discovery of 40 new globular clusters (GCs) that have been found in surveys of the halo of M31 based on INT/WFC and CHFT/Megacam imagery. A subset of these these new GCs are of an extended, diffuse nature, and include those already found in Huxor et al. (2005). The search strategy is described and basic positional and V and I photometric data are presented for each cluster. For a subset of these clusters, K-band photometry is also given. The new clusters continue to be found to the limit of the survey area (~100 kpc), revealing that the GC system of M31 is much more extended than previously realised. The new clusters increase the total number of confirmed GCs in M31 by approximately 10% and the number of confirmed GCs beyond 1 degree (~14 kpc) by more than 75%. We have also used the survey imagery as well recent HST archival data to update the Revised Bologna Catalogue (RBC) of M31 globular clusters.Comment: Accepted to MNRA

The Specific Globular Cluster Frequencies of Dwarf Elliptical Galaxies from the Hubble Space Telescope

The specific globular cluster frequencies (S_N) for 24 dwarf elliptical (dE) galaxies in the Virgo and Fornax Clusters and the Leo Group imaged with the Hubble Space Telescope are presented. Combining all available data, we find that for nucleated dEs --- which are spatially distributed like giant ellipticals in galaxy clusters --- S_N(dE,N)=6.5 +- 1.2 and S_N increases with M_V, while for non-nucleated dEs --- which are distributed like late-type galaxies --- S_N(dE,noN)=3.1 +- 0.5 and there is little or no trend with M_V. The S_N values for dE galaxies are thus on average significantly higher than those for late-type galaxies, which have S_N < 1. This suggests that dE galaxies are more akin to giant Es than to late-type galaxies. If there are dormant or stripped irregulars hiding among the dE population, they are likely to be among the non-nucleated dEs. Furthermore, the similarities in the properties of the globular clusters and in the spatial distributions of dE,Ns and giant Es suggest that neither galaxy mass or galaxy metallicity is responsible for high values of S_N. Instead, most metal-poor GCs may have formed in dwarf-sized fragments that merged into larger galaxies.Comment: 12 pages (uses aaspp4.sty), 2 figures, 1 table, to appear in the Astrophysical Journa

Chandra Studies of the X-ray Point Source Luminosity Functions of M31

Three different M31 disk fields, spanning a range of stellar populations, were observed by Chandra. We report the X-ray point source luminosity function (LF) of each region, and the LF of M31's globular clusters, and compare these with each other and with the LF of the galaxy's bulge. To interpret the results we also consider tracers of the stellar population, such as OB associations and supernova remnants. We find differences in the LFs among the fields, but cannot definitively relate them to the stellar content of the fields. We find that stellar population information, average and maximum source luminosities, X-ray source densities, and slopes of the LF are useful in combination.Comment: 7 pages, 3 figures, accepted for publication in ApJ. Higher-resolution figures available on reques

How to Assess the Carbon Footprint of a Large University? The Case Study of University of Bologna’s Multicampus Organization

University campuses represent a heterogeneous ecosystem as to social, economic, energetic, and personal travel planning with a huge impact on hosting cities and territories. Sustainable policies are thus fundamental to reduce this impact and to adopt ecological behaviors. The measures for any University Sustainability Plan should be evaluated in terms of GHG emissions, as well as the overall impact of the university itself. Carbon footprint (CF) calculation is a relevant Decision Support tool that allows university organizations to measure and communicate the environmental effects of their activities. The aim of this paper is to present a carbon footprint methodology specifically designed to calculate the carbon footprint of large universities. The methodology was applied to calculate the CF of the University of Bologna by following international standards—i.e., the GHG protocol, the ISO 14064, and the ISO/TR 14069 guide—to understand the environmental impact caused by greenhouse gas emissions from direct and indirect university activities. The study was conducted upon the data available in 2020 and then was compared to the 2018 data, with the aim to recognize if the effect of the pandemic could have altered the results. In 2020, the University of Bologna emitted 16,467 tCO2e which became 15,753 tCO2e considering the offset and avoided emission provided by the internal production of energy from renewable sources. Comparison between 2020 and 2018 shows how, in 2018, most of the emissions came from transportation, representing 74% of the total emissions, while in 2020 almost 50% of total emissions derived by IT procurements. The case application demonstrates the way with which the methodology may be applied to assess environmental impact for complex university campuses

WFPC2 Observations of Massive and Compact Young Star Clusters in M31

We present color magnitude diagrams of four blue massive and compact star clusters in M31: G38, G44, G94, and G293. The diagrams of the four clusters reveal a well-populated upper main sequence and various numbers of supergiants. The U-B and B-V colors of the upper main sequence stars are used to determine reddening estimates of the different lines of sight in the M31 disk. Reddening values range from E(B-V) = 0.20 +/- 0.10 to 0.31 +/- 0.11. We statistically remove field stars on the basis of completeness, magnitude and color. Isochrone fits to the field-subtracted, reddening-corrected diagrams yield age estimates ranging from 63 +/- 15 Myr to 160 +/- 60 Myr. Implications for the recent evolution of the disk near NGC 206 are discussed.Comment: 17 pages, Latex, ApJ, in Pres