A panoramic VISTA of the stellar halo of NGC 253

Outskirts of large galaxies contain important information about the galaxy formation and assembly process, and resolved star count studies can probe the extremely low surface brightness of the outer halos. We use images obtained with the VISTA telescope to construct spatially resolved J vs Z-J colour-magnitude diagrams (CMDs) of NGC 253, a nearly edge-on disk galaxy in the Sculptor group. The very deep photometry, down to J ~ 23.5, and the wide area covered allows us to trace the red giant branch (RGB) and asymptotic giant branch (AGB) stars that belong to the outer disk and the halo of NGC 253, out to 50 kpc along the galaxy minor axis. We confirm the existence of an extra planar stellar component of the disk, with a very prominent southern shelf and a symmetrical feature on the north side. The only additional visible sub-structure is an overdensity in the north-west part of the halo at about 28 kpc from the plane and extending over ~ 20 kpc parallel with the disk of the galaxy. From the stellar count profile along the major axis we measure the transition from the disk to the halo at a radial distance of about 25 kpc, where a clear break appears in the number density profile. The isodensity contours show that the inner halo is a flattened structure that blends with a more extended, diffuse, rounder outer halo. Such external structure can be traced to the very edge of our image out to 50 kpc from the disk plane. The number density profile of the stars in the stellar halo follows a power law with index -1.6, as function of radius. The CMD shows a very homogeneous stellar population across the whole field; by comparison with theoretical isochrones we conclude that the RGB stars are ~ 8 Gyr old or more, while the AGB stars trace a population of about 2 x 10^8 Mo, formed from ~ 0.5 to a few Gyr ago. Surprisingly, part of this latter population appears scattered over a wide area.Comment: To appear on Astronomy and Astrophysic

The NIR structure of the barred galaxy NGC253 from VISTA

[abridged] We used J and Ks band images acquired with the VISTA telescope as part of the science verification to quantify the structures in the stellar disk of the barred Sc galaxy NGC253. Moving outward from the galaxy center, we find a nuclear ring within the bright 1 kpc diameter nucleus, then a bar, a ring with 2.9 kpc radius. From the Ks image we obtain a new measure of the deprojected length of the bar of 2.5 kpc. The bar's strength, as derived from the curvature of the dust lanes in the J-Ks image, is typical of weak bars. From the deprojected length of the bar, we establish the corotation radius (R_CR=3 kpc) and bar pattern speed (Omega_b = 61.3 km /s kpc), which provides the connection between the high-frequency structures in the disk and the orbital resonances induced by the bar. The nuclear ring is located at the inner Lindblad resonance. The second ring does not have a resonant origin, but it could be a merger remnant or a transient structure formed during an intermediate stage of the bar formation. The inferred bar pattern speed places the outer Lindblad resonance within the optical disk at 4.9 kpc, in the same radial range as the peak in the HI surface density. The disk of NGC253 has a down-bending profile with a break at R~9.3 kpc, which corresponds to about 3 times the scale length of the inner disk. We discuss the evidence for a threshold in star formation efficiency as a possible explanation of the steep gradient in the surface brightness profile at large radii. The NIR photometry unveils the dynamical response of the NGC253 stellar disk to its central bar. The formation of the bar may be related to the merger event that determined the truncation of stars and gas at large radii and the perturbation of the disk's outer edge.Comment: Accepted for publication in Astronomy & Astrphysics. High resolution pdf file is available at the following link: https://www.dropbox.com/s/4o4cofs1lyjrtpv/NGC253.pd

Field Study of Potential Relocation Sites for the Adams County Farmers’ Market

Farmers markets are an essential part of a community\u27s culture and provide a vital service to all of its members. Currently, the Adam’s County Farmers Market is at a crossroads, as the lease it has on its current location is up and they must consider where they will go next. The purpose of this study is to assist the market in finding the best location in Gettysburg by analyzing the potential sites and providing a numerical score to compare each site. Four potential locations were used in this study: Constitution Lot, Lutheran Seminary, Recreation Park and the Existing site location. Of these locations it was hypothesized that Recreation Park would be the best spot due to its many open fields and provided amenities. The study was conducted by identifying 12 criteria to consider for each site and weighting them against each other using an Analytical Hierarchy Process (AHP). Each site was given a score for each category and each weight was applied to the corresponding category. These scores were added up and each site received a score out of four measuring the quality of the site. The highest scoring site was Constitution Lot followed by the Existing Site, Recreation Park, and Lutheran Seminary. The Constitution Lot site benefited greatly from its vendor and parking space size while the Existing site location came in at a close second due to its many amenities. This study was conducted with the hope of improving the quality of the farmer’s market and increasing its vendor capabilities so that it can better serve the community

An Ultra diffuse Galaxy in the NGC 5846 group from the VEGAS survey

Many ultra diffuse galaxies (UDGs) have now been identified in clusters of galaxies. However, the number of nearby UDGs suitable for detailed follow-up remain rare. Our aim is to begin to identify UDGs in the environments of nearby bright early-type galaxies from the VEGAS survey. Here we use a deep g band image of the NGC 5846 group, taken as part of the VEGAS survey, to search for UDGs. We found one object with properties of a UDG if it associated with the NGC 5846 group, which seems likely. The galaxy, we name NGC 5846$\_$UDG1, has an absolute magnitude of M$_g$ = -14.2, corresponding to a stellar mass of $\sim$10$^8$ M$_{\odot}$. It also reveals a system of compact sources which are likely globular clusters. Based on the number of globular clusters detected we estimate a halo mass that is greater than 8$\times$10$^{10}$ M$_{\odot}$ for UDG1.Comment: 5 pages, 4 figures, accepted for publication in A&

The Halo Shape and Evolution of Polar Disc Galaxies

We examine the properties and evolution of a simulated polar disc galaxy. This galaxy is comprised of two orthogonal discs, one of which contains old stars (old stellar disc), and the other, containing both younger stars and the cold gas (polar disc) of the galaxy. By exploring the shape of the inner region of the dark matter halo, we are able to confirm that the halo shape is a oblate ellipsoid flattened in the direction of the polar disc. We also note that there is a twist in the shape profile, where the innermost 3 kpc of the halo flattens in the direction perpendicular to the old disc, and then aligns with the polar disc out until the virial radius. This result is then compared to the halo shape inferred from the circular velocities of the two discs. We also use the temporal information of the simulation to track the system's evolution, and identify the processes which give rise to this unusual galaxy type. We confirm the proposal that the polar disc galaxy is the result of the last major merger, where the angular moment of the interaction is orthogonal to the angle of the infalling gas. This merger is followed by the resumption of coherent gas infall. We emphasise that the disc is rapidly restored after the major merger and that after this event the galaxy begins to tilt. A significant proportion of the infalling gas comes from filaments. This infalling gas from the filament gives the gas its angular momentum, and, in the case of the polar disc galaxy, the direction of the gas filament does not change before or after the last major merger.Comment: Accepted for publication in MNRAS; 14 pages; 14 figure

The Fornax Deep Survey with VST. VIII. Connecting the accretion history with the cluster density

This work is based on deep multi-band (g, r, i) data from the Fornax Deep Survey with VST. We analyse the surface brightness profiles of the 19 bright ETGs inside the virial radius of the Fornax cluster. The main aim of this work is to identify signatures of accretion onto galaxies by studying the presence of outer stellar halos, and understand their nature and occurrence. Our analysis also provides a new and accurate estimate of the intra-cluster light inside the virial radius of Fornax. We performed multi-component fits to the azimuthally averaged surface brightness profiles available for all sample galaxies. This allows to quantify the relative weight of all components in the galaxy structure that contribute to the total light. In addition, we derived the average g-i colours in each component identified by the fit, as well as the azimuthally averaged g-i colour profiles, to correlate them with the stellar mass of each galaxy and the location inside the cluster. We find that in the most massive and reddest ETGs the fraction of light in, probably accreted, halos is much larger than in the other galaxies. Less-massive galaxies have an accreted mass fraction lower than 30%, bluer colours and reside in the low-density regions of the cluster. Inside the virial radius of the cluster, the total luminosity of the intra-cluster light, compared with the total luminosity of all cluster members, is about 34%. Inside the Fornax cluster there is a clear correlation between the amount of accreted material in the stellar halos of galaxies and the density of the environment in which those galaxies reside. By comparing this quantity with theoretical predictions and previous observational estimates, there is a clear indication that the driving factor for the accretion process is the total stellar mass of the galaxy, in agreement with the hierarchical accretion scenario.Comment: 18 pages, 10 figures. Accepted for publication in A&

Stellar kinematics for the central spheroid in the Polar Disk Galaxy NGC4650A

We have obtained high angular resolution, high signal-to-noise spectra of the Calcium triplet absorption lines on the photometric axes of the stellar spheroid in the polar disk galaxy NGC4650A. Along the major axis, the observed rotation and velocity dispersion measurements show the presence of a kinematically decoupled nucleus, and a flat velocity dispersion profile. The minor axis kinematics is determined for the first time: along this direction some rotation is measured, and the velocity dispersion is nearly constant and slightly increases at larger distances from the center. The new high resolution kinematic data suggest that the stellar component in NGC4650A resembles a nearly-exponential oblate spheroid supported by rotation. The main implications of these results on the previous mass models for NGC4650A are discussed. Moreover, the new kinematic data set constraints on current models for the formation scenarios of Polar Ring Galaxies (PRGs), supporting a slow accretion rather then a secondary strong dissipative event.Comment: 25 pages, 8 figures, accepted for publication in the Astrophysical Journa

Near-Infrared photometry in the J, H and Kn bands for Polar Ring Galaxies: I. Data, structural parameters

We present new Near-Infrared (NIR) observations, in the J, H and Kn bands, for a sample of Polar Ring Galaxies (PRGs), selected from the Polar Ring Catalogue (Whitmore et al. 1990). Data were acquired with the CASPIR near-IR camera at the 2.3 m telescope of Mount Stromlo and Siding Spring Observatory. We report here on the detail morphological study for the central host galaxy and the polar structure in all PRGs of our sample. Total magnitudes, bulge-to-disk decomposition and structural parameters are computed for all objects. These data are crucial for an accurate modeling of the stellar population and the estimate of the star formation rates in the two components.Comment: 14 pages, 8 postscript figures, accepted for publication in A&A. For high resolution Figure 1 and Figure 4, see http://www.na.astro.it/~enric