The Stromlo Missing Satellites Survey

The Stromlo Missing Satellites (SMS) program is a critical endeavor to investigate whether cold dark matter cosmology is flawed in its ability to describe the matter distribution on galaxy scales or proves itself once again as a powerful theory to make observational predictions. The project will deliver unprecedented results on Milky Way satellite numbers, their distribution and physical properties. It is the deepest, most extended survey for optically elusive dwarf satellite galaxies to date, covering the entire 20,000 sq deg of the Southern hemisphere. 150TB of CCD images will be analysed in six photometric bands, 0.5-1.0 mag fainter than SDSS produced by the ANU SkyMapper telescope over the next five years. (For more details see: http://msowww.anu.edu.au/~jerjen/SMS_Survey.html)Comment: 4 pages, 1 figure, in "Galaxies in the Local Volume" (Sydney, 8-13 July 2007), eds B. Koribalski and H. Jerjen, Springer Astrophysics and Space Science Proceedings, p. 18

Formation and structure of halos in a warm dark matter cosmology

(Abridged) Using high-resolution cosmological N-body simulations, we study how the density profiles of dark matter halos are affected by the filtering of the density power spectrum below a given scale length and by the introduction of a thermal velocity dispersion. In the warm dark matter (WDM) scenario, both the free-streaming scale, R_f, and the velocity dispersion, v_w, are determined by the mass m_w of the WDM particle. We find that v_w is too small to affect the density profiles of WDM halos. Down to the resolution attained in our simulations, there is not any significant difference in the density profiles and concentrations of halos obtained in simulations with and without the inclusion of v_w. The density profiles of halos with masses down to ~0.01 the filtering mass M_f can be described by the NFW shape; significant soft cores are not formed. Nevertheless, the concentrations of these halos are lower than those of the CDM counterparts and are approximately independent of mass. The lower concentrations of WDM halos with respect to their CDM counterparts can be accounted for their late formation epoch. Overall, our results point to a series of advantages of a WDM model over the CDM one. In addition to solving the substructure problem, a WDM model with R_f~0.16 Mpc (m_w~0.75 kev; flat cosmology with Omega_L=h=0.7) also predicts concentrations, a Tully-Fisher relation, and formation epochs for small halos which seems to be in better agreement with observations, relative to CDM predictions.Comment: Accepted for publication in ApJ. 34 pages, figs. 1a,1b, and 1c given in separate files (high resolution versions available at ftp://ftp.astroscu.unam.mx/pub/temporal/). Major modifications after referees Report (more simulations and new figures are presented), but main conclusions remain the sam

AN ULTRA-FAINT GALAXY CANDIDATE DISCOVERED in EARLY DATA from the MAGELLANIC SATELLITES SURVEY

We report a new ultra-faint stellar system found in Dark Energy Camera data from the first observing run of the Magellanic Satellites Survey (MagLiteS). MagLiteS J0644-5953 (Pictor II or Pic II) is a low surface brightness (μ = 28.5+1 -1 mag arcsec-2 within its half-light radius) resolved overdensity of old and metal-poor stars located at a heliocentric distance of 45+5 -4 kpc. The physical size (r1/2 = 46+15 -11) and low luminosity (Mv = -3.2+0.4 -0.5 mag) of this satellite are consistent with the locus of spectroscopically confirmed ultra-faint galaxies. MagLiteS J0644-5953 (Pic II) is located 11.3+3.1 -0.9 kpc from the Large Magellanic Cloud (LMC), and comparisons with simulation results in the literature suggest that this satellite was likely accreted with the LMC. The close proximity of MagLiteS J0644-5953 (Pic II) to the LMC also makes it the most likely ultra-faint galaxy candidate to still be gravitationally bound to the LMC.Peer reviewe

A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy: VI. s-Process and Titanium Abundance Variations Along the Sagittarius Stream

We present high-resolution spectroscopic measurements of the abundances of titanium (Ti), yttrium (Y) and lanthanum (La) for M giant candidates of the Sagittarius (Sgr) dwarf spheroidal (dSph) + tidal tail system pre-selected on the basis of position and radial velocity. The majority of these stars show peculiar abundance patterns compared to those of nominal Milky Way (MW) stars. The overall [Ti/Fe], [Y/Fe], [La/Fe] and [La/Y] patterns with [Fe/H] of the Sgr stream plus Sgr core do resemble those seen in the Large Magellanic Cloud (LMC) and other dSphs, only shifted [Fe/H] by ~+0.4 from the LMC and by ~+1 dex from the other dSphs; these relative shifts reflect the faster and/or more efficient chemical evolution of Sgr compared to the other satellites, and show that Sgr has had an enrichment history more like the LMC than the other dSphs. By tracking the evolution of the abundance patterns along the Sgr stream we can follow the time variation of the chemical make-up of dSph stars donated to the MW halo by Sgr. This evolution demonstrates that while the bulk of the stars currently in the Sgr dSph are quite unlike those of the MW halo, an increasing number of stars farther along the Sgr stream have abundances like MW halo stars, a trend that shows clearly how the MW halo could have been contributed by present day satellite galaxies even if the present chemistry of those satellites is now different from typical halo field stars. Finally, we analyze the chemical abundances of a moving group of M giants among the Sgr leading arm stars at the North Galactic Cap, but having radial velocities unlike the infalling Sgr leading arm debris there. Through use of "chemical fingerprinting", we conclude that these northern hemisphere M giants also are Sgr stars, likely trailing arm debris overlapping the leading arm in the north.Comment: Accepted for publication in Ap

Toward an internally consistent astronomical distance scale

Accurate astronomical distance determination is crucial for all fields in astrophysics, from Galactic to cosmological scales. Despite, or perhaps because of, significant efforts to determine accurate distances, using a wide range of methods, tracers, and techniques, an internally consistent astronomical distance framework has not yet been established. We review current efforts to homogenize the Local Group's distance framework, with particular emphasis on the potential of RR Lyrae stars as distance indicators, and attempt to extend this in an internally consistent manner to cosmological distances. Calibration based on Type Ia supernovae and distance determinations based on gravitational lensing represent particularly promising approaches. We provide a positive outlook to improvements to the status quo expected from future surveys, missions, and facilities. Astronomical distance determination has clearly reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press (chapter 8 of a special collection resulting from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space Age

A review of elliptical and disc galaxy structure, and modern scaling laws

A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their models to describe the radial distribution of stars in `nebulae'. This article reviews the progress since then, providing both an historical perspective and a contemporary review of the stellar structure of bulges, discs and elliptical galaxies. The quantification of galaxy nuclei, such as central mass deficits and excess nuclear light, plus the structure of dark matter halos and cD galaxy envelopes, are discussed. Issues pertaining to spiral galaxies including dust, bulge-to-disc ratios, bulgeless galaxies, bars and the identification of pseudobulges are also reviewed. An array of modern scaling relations involving sizes, luminosities, surface brightnesses and stellar concentrations are presented, many of which are shown to be curved. These 'redshift zero' relations not only quantify the behavior and nature of galaxies in the Universe today, but are the modern benchmark for evolutionary studies of galaxies, whether based on observations, N-body-simulations or semi-analytical modelling. For example, it is shown that some of the recently discovered compact elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to appear in "Planets, Stars and Stellar Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references incl. many somewhat forgotten, pioneer papers. Original submission to Springer: 07-June-201

Magellan/M2FS Spectroscopy of Tucana 2 and Grus 1

We present results from spectroscopic observations with the Michigan/Magellan Fiber System (M2FS) of $147$ stellar targets along the line of sight to the newly-discovered `ultrafaint' stellar systems Tucana 2 (Tuc 2) and Grus 1 (Gru 1). Based on simultaneous estimates of line-of-sight velocity and stellar-atmospheric parameters, we identify 8 and 7 stars as probable members of Tuc 2 and and Gru 1, respectively. Our sample for Tuc 2 is sufficient to resolve an internal velocity dispersion of $8.6_{-2.7}^{+4.4}$ km s$^{-1}$ about a mean of $-129.1_{-3.5}^{+3.5}$ km s$^{-1}$ (solar rest frame), and to estimate a mean metallicity of [Fe/H]= $-2.23_{-0.12}^{+0.18}$. These results place Tuc 2 on chemodynamical scaling relations followed by dwarf galaxies, suggesting a dominant dark matter component with dynamical mass $2.7_{-1.3}^{+3.1}\times 10^6$ $\mathrm{M}_{\odot}$ enclosed within the central $\sim 160$ pc, and dynamical mass-to-light ratio $1900_{-900}^{+2200}$ $\mathrm{M}_{\odot}/L_{V,\odot}$. For Gru 1 we estimate a mean velocity of $-140.5_{-1.6}^{+2.4}$ km s$^{-1}$ and a mean metallicity of [Fe/H]=$-1.42_{-0.42}^{+0.55}$, but our sample does not resolve Gru 1's velocity dispersion. The radial coordinates of Tuc 2 and Gru 1 in Galactic phase space suggest that their orbits are among the most energetic within distance $\leq 300$ kpc. Moreover, their proximity to each other in this space arises naturally if both objects are trailing the Large Magellanic Cloud.Comment: replaced with ApJ-accepted version, all spectra and data products (including samples from posterior PDFs) are available at http://www.andrew.cmu.edu/user/mgwalker/tuc2gru1_dataproducts.tar.g

Kinematics and chemistry of recently discovered Reticulum 2 and Horologium 1 dwarf galaxies

Photometry alone is not sufficient to unambiguously distinguish between ultra-faint star clusters and dwarf galaxies because of their overlap in morphological properties. Here we report on VLT/GIRAFFE spectra of candidate member stars in two recently discovered ultra-faint satellites Reticulum 2 and Horologium 1, obtained as part of the ongoing Gaia-ESO Survey. We identify 18 members in Reticulum 2 and 5 in Horologium 1. We find Reticulum 2 to have a velocity dispersion of ~3.22 km/s, implying a M/L ratio of ~ 500. We have inferred stellar parameters for all candidates and we find Reticulum 2 to have a mean metallicity of [Fe/H] = -2.46+/-0.1, with an intrinsic dispersion of ~ 0.29, and is alpha-enhanced to the level of [alpha/Fe]~0.4. We conclude that Reticulum 2 is a dwarf galaxy. We also report on the serendipitous discovery of four stars in a previously unknown stellar substructure near Reticulum 2 with [Fe/H] ~ -2 and V_hel ~ 220 km/s, far from the systemic velocity of Reticulum 2. For Horologium 1 we infer a velocity dispersion of 4.9^{+2.8}_{-0.9} km/s and a consequent M/L ratio of ~ 600, leading us to conclude that Horologium 1 is also a dwarf galaxy. Horologium 1 is slightly more metal-poor than Reticulum 2 [Fe/H] = -2.76 +/- 0.1 and is similarly alpha-enhanced: [alpha/Fe] ~ 0.3. Despite a large error-bar, we also measure a significant spread of metallicities of 0.17 dex which strengthen the evidence that Horologium 1 is indeed a dwarf galaxy. The line-of-sight velocity of Reticulum 2 is offset by some 100 km/s from the prediction of the orbital velocity of the LMC, thus making its association with the Cloud uncertain. However, at the location of Horologium 1, both the backward integrated LMC's orbit and the LMC's halo are predicted to have radial velocities similar to that of the dwarf. Therefore, it is likely that Horologium 1 is or once was a member of the Magellanic Family.Comment: submitted to ApJ, abstract abridge

BEASTS OF THE SOUTHERN WILD: DISCOVERY OF NINE ULTRA FAINT SATELLITES IN THE VICINITY OF THE MAGELLANIC CLOUDS

We have used the publicly released Dark Energy Survey data to hunt for new satellites of the Milky Way in the Southern hemisphere. Our search yielded a large number of promising candidates. In this paper, we announce the discovery of 9 new unambiguous ultra-faint objects, whose authenticity can be established with the DES data alone. Based on the morphological properties, three of the new satellites are dwarf galaxies, one of which is located at the very outskirts of the Milky Way, at a distance of 380 kpc. The remaining 6 objects have sizes and luminosities comparable to the Segue~1 satellite and can not be classified straightforwardly without follow-up spectroscopic observations. The satellites we have discovered cluster around the LMC and the SMC. We show that such spatial distribution is unlikely under the assumption of isotropy, and, therefore, conclude that at least some of the new satellites must have been associated with the Magellanic Clouds in the past.Comment: Accepted to ApJ; See also 1503.02584; Changes w.r.t. v2: the discussion section updated slightly; small changes in the table with satellite parameter

Large-Scale Spatio-Temporal Patterns of Mediterranean Cephalopod Diversity

Species diversity is widely recognized as an important trait of ecosystems’ functioning and resilience. Understanding the causes of diversity patterns and their interaction with the environmental conditions is essential in order to effectively assess and preserve existing diversity. While diversity patterns of most recurrent groups such as fish are commonly studied, other important taxa such as cephalopods have received less attention. In this work we present spatio-temporal trends of cephalopod diversity across the entire Mediterranean Sea during the last 19 years, analysing data from the annual bottom trawl survey MEDITS conducted by 5 different Mediterranean countries using standardized gears and sampling protocols. The influence of local and regional environmental variability in different Mediterranean regions is analysed applying generalized additive models, using species richness and the Shannon Wiener index as diversity descriptors. While the western basin showed a high diversity, our analyses do not support a steady eastward decrease of diversity as proposed in some previous studies. Instead, high Shannon diversity was also found in the Adriatic and Aegean Seas, and high species richness in the eastern Ionian Sea. Overall diversity did not show any consistent trend over the last two decades. Except in the Adriatic Sea, diversity showed a hump-shaped trend with depth in all regions, being highest between 200–400 m depth. Our results indicate that high Chlorophyll a concentrations and warmer temperatures seem to enhance species diversity, and the influence of these parameters is stronger for richness than for Shannon diversityVersión del editor4,411