Early-type galaxies (ETGs) are observed to be more compact at z>2 than in the local Universe. Remarkably, much of this size evolution appears to take place in a short (1.8 Gyr) time span between z=2.2 and z=1.3, which poses a serious challenge to hierarchical galaxy formation models where mergers occurring on a similar timescale are the main mechanism for galaxy growth. We compute the merger-driven redshift evolution of stellar mass Mstar\propto(1+z)^aM, half-mass radius Re\propto(1+z)^aR and velocity-dispersion sigma0\propto(1+z)^asigma predicted by concordance Lambda cold dark matter for a typical massive ETG in the redshift range z=1.3-2.2. Neglecting dissipative processes, and thus maximizing evolution in surface density, we find -1.5<aM<-0.6, -1.9<aR<-0.7 and 0.06<asigma<0.22, under the assumption that the accreted satellites are spheroids. It follows that the predicted z=2.2 progenitors of z=1.3 ETGs are significantly less compact (on average a factor of 2 larger Re at given Mstar) than the quiescent galaxies observed at z>2. Furthermore, we find that the scatter introduced in the size-mass correlation by the predicted merger-driven growth is difficult to reconcile with the tightness of the observed scaling law. We conclude that - barring unknown systematics or selection biases in the current measurements - minor and major mergers with spheroids are not sufficient to explain the observed size growth of ETGs within the standard model.
The infall of cold dark matter onto a galaxy produces cold collisionless flows and caustics in its halo. If a signal is found in the cavity detector of dark matter axions, the flows will be readily apparent as peaks in the energy spectrum of photons from axion conversion, allowing the densities, velocity vectors and velocity dispersions of the flows to be determined. We discuss the evolution of velocity dispersion along cold collisionless flows in one and two dimensions. A technique is presented for obtaining the leading behaviour of the velocity dispersion near caustics. The results are used …
Massive stars have a strong impact on their local environments. However, how stellar feedback regulates star formation is still under debate. In this context, we studied the chemical properties of 80 dense cores in the Orion molecular cloud complex composed of the Orion A (39 cores), B (26 cores), and lambda Orionis (15 cores) clouds using multiple molecular line data taken with the Korean Very Long Baseline Interferometry Network (KVN) 21-m telescopes. The lambda Orionis cloud has an H ii bubble surrounding the O-type star lambda Ori, and hence it is exposed to the ultraviolet (UV) radiation …
The abundance of dark matter satellites and subhalos, the existence of density cusps at the centers of dark matter halos, and problems producing realistic disk galaxies in simulations are issues that have raised concerns about the viability of the standard cold dark matter (LambdaCDM) scenario for galaxy formation. This talk reviews these issues, and considers the implications for cold vs. various varieties of warm dark matter (WDM). The current evidence appears to be consistent with standard LambdaCDM, although improving data may point toward a rather tepid version of LambdaWDM - tepid since …
The dwarf galaxies around the Milky Way are distributed in a so-called vast polar structure (VPOS) that may be in conflict with Lambda CDM simulations. Here, we seek to determine if the VPOS poses a serious challenge to the Lambda cold dark matter paradigm on galactic scales. Specifically, we investigate if the VPOS remains coherent as a function of time. Using the measured Hubble Space Telescope (HST) proper motions and associated uncertainties, we integrate the orbits of the classical Milky Way satellites backwards in time and find that the structure disperses well before a dynamical time. W…
Observations have revealed cold gas with large velocity dispersions (~300 km/s) within the hot outflows of ultra-luminous infrared galaxies (ULIRGs). This gas may trace its origin to the Rayleigh-Taylor (RT) fragmentation of a super-bubble or may arise on smaller scales. We model a ULIRG outflow at two scales to recreate this gas in three-dimensional hydrodynamic simulations using FLASH. Although resolution is limited, these models successfully produce cold gas in outflows with large velocity dispersions. Our small-scale models produce this cold gas through RT fragmentation of the super-bubble…
We present Bayesian AGN Decomposition Analysis for SDSS Spectra (BADASS), an open source spectral analysis code designed for automatic detailed deconvolution of AGN and host galaxy spectra, implemented in Python, and designed for the next generation of large scale surveys. BADASS simultaneously fits all spectral components, including power-law continuum, stellar line-of-sight velocity distribution, FeII emission, as well as forbidden (narrow), permitted (broad), and outflow emission line features, all performed using Markov Chain Monte Carlo to obtain robust uncertainties and autocorrelation a…
We report the detection of the propargyl radical (CH2CCH) in the cold dark cloud TMC-1 in the lambda 3 mm wavelength band. We recently discovered this species in space toward the same source at a wavelength of lambda 8 mm. In those observations, various hyperfine components of the 2,0,2-1,0,1 rotational transition, at 37.5 GHz, were detected using the Yebes 40m telescope. Here, we used the IRAM 30m telescope to detect ten hyperfine components of the 5,0,5-4,0,4 rotational transition, lying at 93.6 GHz. The observed frequencies differ by 0.2 MHz with respect to the predictions from available la…
The Sculptor dwarf spheroidal galaxy contains two distinct stellar populations: one metal-rich and the other metal-poor. Several authors have argued that in order for these two populations to reside in the same gravitational potential, the dark matter halo must have a core similar to that observed in the stellar count profile. This would rule out the cuspy Navarro-Frenk-White (NFW) density profiles predicted for halos and subhalos by dark matter only simulations of the Lambda Cold Dark Matter (Lambda-CDM) cosmological model. We present a new theoretical framework to analyse stellar count and v…
We use the "Evolution and Assembly of GaLaxies and their Environments" ( EAGLE ) suite of hydrodynamical cosmological simulations to measure offsets between the centres of stellar and dark matter components of galaxies. We find that the vast majority (>95%) of the simulated galaxies display an offset smaller than the gravitational softening length of the simulations (Plummer-equivalent $ε= 700$ pc), both for field galaxies and satellites in clusters and groups. We also find no systematic trailing or leading of the dark matter along a galaxy's direction of motion. The offsets are consistent wit…
(Abridged) Extensions of the standard model of particle physics predict very light bosons, ranging from about 10^{-5} eV for the QCD axion to 10^{-33} eV for ultra-light particles, which could be the cold dark matter (CDM) in the Universe. If so, their phase-space density must be high enough to form a Bose-Einstein condensate (BEC). The fluid-like nature of BEC-CDM dynamics differs from that of standard collisionless CDM (sCDM), so observations of galactic haloes may distinguish them. sCDM has problems with galaxy observations on small scales, which BEC-CDM may overcome for a large range of pa…
In the widely adopted LambdaCDM scenario for galaxy formation, dwarf galaxies are the building blocks of larger galaxies. Since they formed at relatively early epochs when the background density was relatively high, they are expected to retain their integrity as satellite galaxies when they merge to form larger entities. Although many dwarf spheroidal galaxies (dSphs) are found in the galactic halo around the Milky Way, their phase space density (or velocity dispersion) appears to be significantly smaller than that expected for satellite dwarf galaxies in the LambdaCDM scenario. In order to ac…
We analyse the dark, gas, and stellar mass assembly histories of low-mass halos (Mvir ~ 10^10.3 - 10^12.3 M_sun) identified at redshift z = 0 in cosmological numerical simulations. Our results indicate that for halos in a given present-day mass bin, the gas-to-baryon fraction inside the virial radius does not evolve significantly with time, ranging from ~0.8 for smaller halos to ~0.5 for the largest ones. Most of the baryons are located actually not in the galaxies but in the intrahalo gas; for the more massive halos, the intrahalo gas-to-galaxy mass ratio is approximately the same at all reds…
Gas velocity dispersions provide important diagnostics of the forces counteracting gravity to prevent collapse of the gas. We use the 21 cm line of neutral atomic hydrogen (HI) to study HI velocity dispersion and HI phases as a function of galaxy morphology in 22 galaxies from The HI Nearby Galaxy Survey (THINGS). We stack individual HI velocity profiles and decompose them into broad and narrow Gaussian components. We study the HI velocity dispersion and the HI surface density, as a function of radius. For spirals, the velocity dispersions of the narrow and broad components decline with radius…
Observations of stars in the the solar vicinity show a clear tendency for old stars to have larger velocity dispersions. This relation is called the age-velocity dispersion relation (AVR) and it is believed to provide insight into the heating history of the Milky Way galaxy. Here, in order to investigate the origin of the AVR, we performed smoothed particle hydrodynamic simulations of the self-gravitating multiphase gas disks in the static disk-halo potentials. Star formation from cold and dense gas is taken into account, and we analyze the evolution of these star particles. We find that expon…
In decomposing the HI rotation curves of disc galaxies, it is necessary to break a degeneracy between the gravitational fields of the disc and the dark halo by estimating the disc surface density. This is done by combining measurements of the vertical velocity dispersion of the disc with the disc scale height. The vertical velocity dispersion of the discs is measured from absorption lines (near the V-band) of near-face-on spiral galaxies, with the light coming from a mixed population of giants of all ages. However, the scale heights for these galaxies are estimated statistically from near-IR s…
The Doppler effect is commonly used to infer the velocity difference between stars based on the relative shifts in the rest-frame wavelengths of their spectral features. In dynamically-cold systems with a low velocity dispersion, such as wide binaries, loose star clusters, cold stellar streams or cosmological mini-halos, the scatter in the gravitational redshift from the surface of the constituent stars needs to be taken into account as well. Gravitational redshifts could be important for wide binaries composed of main sequence stars with separations >0.01 pc or in mini-halos with velocity dis…
Context: We present COSTA (COld STream finder Algorithm), a novel algorithm to search for cold kinematical substructures in the phase space of planetary nebulae (PNe) and globular clusters (GCs) in the halo of massive galaxies and intracluster regions. Aims: COSTA aims at detecting small sized, low velocity dispersion streams, as the ones produced in recent interactions of dwarf galaxies with the halo of more massive galaxies, including the ones sitting in the central region of rich galaxy clusters. Methods: COSTA is based on a deep friend-of-friend procedure that isolates groups of N particle…
The COld STream finder Algorithm (COSTA) is a novel algorithm to find streams in the phase space of planetary nebulae (PNe) and globular cluster (GCs) populations. COSTA isolates groups of particles with small velocity dispersion, using an iterative sigma-clipping over a defined number of neighbor particles. We have applied COSTA to a catalog of about 2000 PNe and GCs from the Fornax Cluster VLT Spectroscopic Survey (FVSS), within 200 kpc from the cluster core, to detect cold substructures and characterize their kinematics. We have found 13 cold substructures, with velocity dispersion ranging …
We present results from MMT/Hectochelle spectroscopy of red giant candidate stars along the line of sight to the recently-discovered Galactic satellite Crater 2. Modelling the joint distribution of stellar positions, velocities and metallicities as a mixture of Crater 2 and Galactic foreground populations, we identify 62 members of Crater 2, for which we resolve line-of-sight velocity dispersion 2.7 +/- 0.3 km/s about mean velocity of 87.5 +/- 0.4 km/s. We also resolve a metallicity dispersion 0.22 about a mean of [Fe/H]=-1.98 +/- 0.1 that is 0.28 +/- 0.14 poorer than is estimated from photome…
Although highly successful on cosmological scales, Cold Dark Matter (CDM) models predict unobserved over-dense `cusps' in dwarf galaxies and overestimate their formation rate. We consider an ultra-light axion-like scalar boson which promises to reduce these observational discrepancies at galactic scales. The model, known as Fuzzy Dark Matter (FDM), avoids cusps, suppresses small-scale power, and delays galaxy formation via macroscopic quantum pressure. We compare the substructure and density fluctuations of galactic dark matter haloes comprised of ultra-light axions to conventional CDM results…
NGC 1313 is a bulgeless nearby galaxy, classified as SB(s)d. Its proximity allows high spatial resolution observations. We performed the first detailed analysis of the emission-line properties in the nuclear region of NGC 1313, using an optical data cube obtained with the Gemini Multi-object Spectrograph. We detected four main emitting areas, three of them (regions 1, 2 and 3) having spectra typical of H II regions. Region 1 is located very close to the stellar nucleus and shows broad spectral features characteristic of Wolf-Rayet stars. Our analysis revealed the presence of one or two WC4-5 s…
