S. N. Kemp

Spitzer mid-infrared spectroscopic observations of planetary nebulae

We present Spitzer Space Telescope archival mid-infrared (mid-IR) spectroscopy of a sample of eleven planetary nebulae (PNe). The observations, acquired with the Spitzer Infrared Spectrograph (IRS), cover the spectral range 5.2-14.5 {\mu}m that includes the H2 0-0 S(2) to S(7) rotational emission lines. This wavelength coverage has allowed us to derive the Boltzmann distribution and calculate the H2 rotational excitation temperature (Tex). The derived excitation temperatures have consistent values ~900+/-70 K for different sources despite their different structural components. We also report the detection of mid-IR ionic lines of [Ar III], [S IV], and [Ne II] in most objects, and polycyclic aromatic hydrocarbon (PAH) features in a few cases. The decline of the [Ar III]/[Ne II] line ratio with the stellar effective temperature can be explained either by a true neon enrichment or by high density circumstellar regions of PNe that presumably descend from higher mass progenitor stars.

How much dark matter is there inside early-type galaxies?

We study the luminous mass as a function of the dynamical mass inside the effective radius (r_e) of early-type galaxies (ETGs) to search for differences between these masses. We assume Newtonian dynamics and that any difference between these masses is due to the presence of dark matter. We use several samples of ETGs -ranging from 19 000 to 98 000 objects- from the ninth data release of the Sloan Digital Sky Survey. We perform Monte Carlo (MC) simulations of galaxy samples and compare them with real samples. The main results are: i) MC simulations show that the distribution of the dynamical vs. luminous mass depends on the mass range where the ETGs are distributed (geometric effect). This dependence is caused by selection effects and intrinsic properties of the ETGs. ii) The amount of dark matter inside r_e is approximately 7% +- 22%. iii) This amount of dark matter is lower than the minimum estimate (10%) found in the literature and four times lower than the average (30%) of literature estimates. However, if we consider the associated error, our estimate is of the order of the literature average.

Dark matter inside early-type galaxies as function of mass and redshift

We study the behaviour of the dynamical and stellar mass inside the effective radius (re) of early-type galaxies (ETGs). We use several samples of ETGs -ranging from 19 000 to 98 000 objects- from the ninth data release of the Sloan Digital Sky Survey. We consider Newtonian dynamics, different light profiles and different Initial Mass Functions (IMF) to calculate the dynamical and stellar mass. We assume that any difference between these two masses is due to dark matter and/or a non Universal IMF. The main results for galaxies in the redshift range 0.0024 < z < 0.3500 and in the dynamical mass range 9.5 < log(M) < 12.5 are: i) A significant part of the intrinsic dispersion of the distribution of dynamical vs. stellar mass is due to redshift. ii) The difference between dynamical and stellar mass increases as a function of dynamical mass and decreases as a function of redshift. iii) The difference between dynamical and stellar mass goes from approximately 0% to 70% of the dynamical mass depending on mass and redshift. iv) These differences could be due to dark matter or a non Universal IMF or a combination of both. v) The amount of dark matter inside ETGs would be equal to or less than the difference between dynamical and stellar mass depending on the impact of the IMF on the stellar mass estimation. vi) The previous results go in the same direction of some results of the Fundamental Plane (FP) found in the literature in the sense that they could be interpreted as an increase of dark matter along the FP and a dependence of the FP on redshift.

The tidal filament of NGC 4660

NGC 4660, in the Virgo cluster, is a well-studied elliptical galaxy which has a strong disk component (D/T approximately 0.2–0.3). The central regions, including the disk component, have stellar populations approximately 12–13 Gyr in age, based on SAURON studies. However, we report the discovery of a long, narrow tidal filament associated with the galaxy, as seen in deep co-added Schmidt plate images and deep CCD frames, implying that the galaxy has undergone a tidal interaction and merger within the last few Gyr. The relative narrowness of the filament implies a wet merger with at least one spiral galaxy involved, but the current state of the system shows little evidence of such. However, a two-component photometric fit using GALFIT shows much bluer colors for the disk component than for the elliptical component, which may represent a residual trace of enhanced star formation in the disk caused by the interaction 1–2 Gyr ago. There are brighter concentrations within the filament that resemble tidal dwarf galaxies, although they are at least 40 times fainter. These concentrations may represent faint, evolved versions of those galaxies. A previously detected stripped satellite galaxy south of the nucleus seen in our residual image may imply that the filament is a tidal stream produced by perigalactic passages of this satellite.

BVRI photometric analysis for the galaxy group NGC 4410

We present a BVRI CCD (Charge Coupled Device) surface photometry analysis of the galaxy group NGC 4410, which contains four galaxies in interaction. Along with our photometric study, we show residual images (after subtracting isophotal models) and unsharp masked images to uncover any hidden structures in this system of galaxies; we have also performed a two-dimensional bulge-disk decomposition for NGC 4410C and D, and a major axis sector profile for NGC 4410A. We have calculated BVRI surface brightnesses and colors within regions such as galaxy centers, bridges, tails and optical knots in the NGC 4410 system, generating B−V color maps and color profiles. The information obtained was used to discover the predominant stellar populations. The colors of the galaxies imply ages of ∼2 × 10 9 to ∼2 × 10 10 years for models using a range of metallicities. The bluer knots and H II regions have colors implying ages of a minimum of 5× 10 8 years, but possibly as high as 3× 10 9 years for stellar populations formed in the interaction. These results lead us to conclude that there is a moderate star formation rate and a tranquil evolving state of the system with a long timescale for interaction, much longer than the typical dynamical timescales of 10 8 years. Although we note that NGC 4410D has a blue nucleus (possible nuclear starburst?), bulge, bar, and short spiral arms, and may be interacting with a H I gas cloud. Some observed structures in NGC 4410A are coincident with previously studied H II regions, a tidal arm and optical/radio knots found in this galaxy. An optical knot E coincident with a radio knot may be an optical synchrotron emission or an H II region. The galaxy NGC 4410B appears to be a boxy giant elliptical with a possible dusty disk embedded (similar to Cen A?) and NGC 4410C is confirmed as a lenticular galaxy.

Optics and the mechanical system of the 62-cm telescope at the Severo Díaz Galindo Observatory in Guadalajara, Jalisco, México

We present the results of a modification performed in the optical system of the 62 cm telescope (f/14.32) at observatory “Severo Díaz Galindo” Universidad de Guadalajara, Mexico. This modification consists of a change of distance between the primary and secondary mirrors from 1020 to 1135 mm. With this, a change in the image plane from 5200 mm to 600 mm, measured from the vertex of the primary mirror, is obtained. The latter allow to get the first astronomical images of The Telescope. This modification was necessary because alignment errors, such as distance between primary and secondary mirrors in the original system were presented. Besides, the telescope has a new accurate and adequate mechanical system installed on November 2011. Details and the first images obtained, are here presented.

The Extended Emission of Ultracompact HII Regions: An Overview and New Observations

Ultracompact (UC) HII regions with Extended Emission (EE) are classical UC HII regions associated with much larger (>1’) structures of ionized gas. The efforts to investigate, detect, and understand if the EE is physically related with the UC emission are few. If they are related, our understanding of UC HII regions may be affected (e.g., in the estimation of ionizing UV photons). Here we present a brief overview of UC HII regions with EE (UC HII+EE) including our most recent effort aimed at searching for UC HII regions associated with extended emission.

The Hot Molecular Core of G12.21–0.10: NH 3 (4, 4) Observations

In de la Fuente (2007; Ph. D. Thesis), the molecular clump associated with the ultracompact HII region G12.21–0.10 was confirmed as a large, hot, dense Hot Molecular Core nearby to the ionized gas. The density was confirmed by comparing low resolution NH3(2,2) and (4,4) VLA observations, with other molecular lines and radio–continuum observations. These results will be presented in detail in a forthcoming paper (de la Fuente et al. in preparation). In these works, for the first time, the spatial location of the Hot Molecular Core is presented. Here we present the NH3(4,4) observations from de la Fuente (2007; Ph. D. Thesis), confirming that the hotter and denser gas in the molecular core lies in a compact structure, of smaller scale than the NH3(2,2) emission.

Colours of the Envelopes of cD Galaxies

We have carried out BVR surface photometry of a sample of 6 cD and cD-like galaxies using the 2.1 m telescope at San Pedro Martir, in general reaching surface brightnesses well into the cD envelope. In the majority of cases no appreciable colour gradient was detected, and the envelope has the same red colour as the central galaxy. In the two cD-like galaxies a redward gradient was observed, although in both these cases no extended envelope was detected, possibly due to contamination from neighbouring galaxies. The centre of NGC 1275 (one of the cD-like galaxies) is bluer due to many regions of active star formation. In two cDs with multiple nuclei (A193 and A2634), no colour gradients or regions of current active star formation were found. These results favour an early, ‘primordial origin’ for the cD envelope, the stellar populations of the envelope being coeval with those of the central elliptical galaxy.

Surface photometry of cD envelopes

We have carried out deep BV R surface photometry of 6 cD and cD-like galaxies using the 2.1-m telescope at San Pedro Mártir, cD galaxies are supergiant galaxies (M > 10M ) with enormous halos (> 100 kpc in radius) surrounding a giant elliptical galaxy, found generally at the centre of rich clusters (Oemler 1976, Schombert 1988). The surface brightness profiles of their halos (envelopes) break from the r law, containing more light at large radii (Schombert (1988)), although a detailed 1 and 2 dimensional analysis of their morphology has yet to be carried out. There have been four main theories as to the origin of cD envelopes (Schombert (1988) and references within), a) stripping of stars from other cluster member galaxies, b) formation of galaxy and envelope at the same time during the formation of the cluster, c) mergers of cluster members, which do not easily explain the high velocity dispersions in the envelopes (∼ 1000 km s−1), d) cooling flows: accumulation of cooling X-ray-emitting ICM gas around the central galaxy. Very red envelopes have been found around some cD’s, and star formation biased towards lowmass stars in cooling flows were invoked to explain these red halos, but the expected very bright near-IR halos were not detected (Joy et al. 1995 and references within). Previous detailed studies of cD galaxies (e.g. Mackie 1992) found a range of colour gradients. Our sample included the cDs in the clusters A193, A426 (NGC 1275), A496, A754, A2634 and A2670. The typical colours of their envelopes are (B − V ) = 1.1 − 1.3 and (V − R) = 0.5 − 0.7. In most cases there is no obvious gradient over the entire radial range studied. In the two cD-like galaxies (A426, A754), a gradient of 0.5 to the red in (B − R) was detected, although no extended envelope was detected (neighbour galaxies make it difficult to follow the profile). For NGC 1275, the central regions are bluer due to many regions of active star formation. In the case of 2 objects with multiple nuclei (A193 and A2634), no colour gradients, nor zones of star formation, were found. In many cases the colours of nearby cluster members are very similar to the cD galaxy. These results favour a primordial origin for the cD envelope. Thus the envelope retains characteristics of the cluster, and its stellar population has evolved similarly to that of the central galaxy. Any changes caused by mergers, interactions, and cooling flows, are temporary. The envelope is dominated by an old stellar population (‘red-and-dead’). The largest galaxies in the universe may well be the first to be fully formed, and this seems to be in agreement with recent ideas of ’downsizing’ in which E/cD galaxies are the first to complete their star formation.