Isotopic fractionation is an important tool for investigating the chemical history of our Solar System. In particular, the isotopic fraction of nitrogen (^14^N/^15^N) is lower in comets and other pristine Solar System bodies with respect to the value measured for the protosolar nebula, suggesting a local chemical enrichment of ^15^N during the formation of the Solar System. Therefore, interferometric studies of nitrogen fractionation in Solar System precursors are needed for us to obtain clues about our astrochemical origins. In this work we have investigated the variation in the ^14^N/^15^N ratio in one of the closest analogues of the environment in which the Solar System was born: the protocluster OMC-2 FIR4. We present the first comparison at high angular resolution between HCN and N_2_H^+^ using interferometric data. We analysed observations of the HCN isotopologues H^13^CN and HC^15^N in the OMC-2 FIR4 protocluster. Specifically, we observed the transitions H^13^CN (1-0) and HC^15^N (1-0) with the NOrthern Extended Millimeter Array (NOEMA) within the context of the IRAM Seeds Of Life In Space (SOLIS) Large Program. We combined our results with analysis of archival data obtained with the Atacama Large Millimeter Array (ALMA) of N_2_H^+^ and its ^15^N isotopologues. Our results show a small regional variation in the ^14^N/^15^N ratio for HCN, from ~250 to 500. The ratios in the central regions of FIR4, where the candidate protostars are located, are largely consistent with one another and within that range (~300). They also show little variation from the part of the protocluster known to harbour a high cosmic-ray ionisation rate to the portion with a lower rate. We also found a small variation in the ^14^N/^15^N ratio of N_2_H^+^ across different regions, from ~200 to ~400. These results suggest that local changes in the physical parameters occurring on the small linear scales probed by our observations in the protocluster do not seem to affect the ^14^N/^15^N ratio in either HCN or N_2_H^+^ and hence that this is independent of the molecule used. Moreover, the high level of irradiation due to cosmic rays does not affect the N fractionation either.
We present a Spitzer Space Telescope imaging survey of the most massive Galactic globular cluster, {omega} Centauri, and investigate stellar mass loss at low metallicity and the intracluster medium (ICM). The survey covers approximately 3.2x the cluster half-mass radius at 3.6, 4.5, 5.8, 8, and 24um, resulting in a catalog of over 40000 point sources in the cluster.
We present a study of the optical spectral properties of 115 ultraluminous infrared galaxies (ULIRGs) in the southern sky. Using the optical spectra obtained at the Cerro Tololo Inter-American Observatory (CTIO) 4m telescope and provided by the Two-degree Field (2dF) Galaxy Redshift Survey and the Six-degree Field (6dF) Galaxy Survey, we measure emission linewidths and fluxes for spectral classification.
We present optical observations of a sample of 57 spiral galaxies and describe the procedures followed to reduce the data. We have obtained images in the optical B and I broad bands, as well as in H{alpha}, with moderate spatial resolution and across wide enough fields to image the complete disks of the galaxies. In addition, we observed 55 of our sample galaxies in the R and eight in the V band, and imaged a subset through a dedicated narrow continuum filter for the H{alpha} line. We describe the data reduction procedures we developed in the course of this work to register, combine and photometrically calibrate each set of images for an individual galaxy. We describe in some detail the procedure used to subtract the continuum emission from our H{alpha} images. In companion papers, we describe near-infrared imaging of the galaxy sample, and present analyses of disk scale lengths, and of properties of bars, rings, and HII regions in the sample galaxies. The images described here will be made available for use by other researchers through the CDS.
We investigated the connection between the mid-infrared (MIR) and optical spectral characteristics in a sample of 82 Type 1 active galactic nuclei (AGNs), observed with Infrared Spectrometer on Spitzer (IRS) and Sloan Digital Sky Survey (SDSS, DR12). We found several interesting correlations between optical and MIR spectral properties: (i) as starburst significators in MIR increase, the equivalent widths (EWs) of optical lines H{beta}NLR and FeII, increase as well; (ii) as MIR spectral index increases, EW([OIII]) decreases, while fractional contribution of AGN (RAGN) is not connected with EW([OIII]); (iii) The log([OIII]5007/H{beta}NLR) ratio is weakly related to the fractional contribution of polycyclic aromatic hydrocarbons (RPAHs). We compare the two different MIR and optical diagnostics for starburst contribution to the overall radiation (RPAH and Baldwin, Philips & Terlevich diagram, respectively). The significant differences between optical and MIR starburst diagnostics were found. The starburst influence to observed correlations between optical and MIR parameters is discussed.
In this paper we present optical and near-infrared finding charts, accurate astrometry (~1") and single-epoch near-infrared photometry for 371 IRAS sources, 96% of those included in the so-called "Arecibo sample of OH/IR stars" (Eder et al., 1988ApJS...66..183E; Lewis et al., 1990ApJ...362..634L; Chengalur et al., 1993, Cat. <J/ApJS/89/189>). The main photometric properties of the stars in the sample are presented and discussed as well as the problems found during the process of identification of the optical/near-infrared counterparts. In addition, we also identify suitable reference stars in each field to be used for differential photometry purposes in the future.
We present an 8-band (u*, g', r', i', z', Y, J, Ks) optical to near-infrared deep photometric catalogue based on the observations made with MegaCam and WIRCam at CFHT, and compute photometric redshifts, zph in the North Ecliptic Pole (NEP) region, where AKARI infrared satellite carried out deep survey at near to mid infrared wavelength. We designed the catalogue to include sources detected in z' band with counterparts in at least one of the other bands, and found 85797 sources in the NEP field. Comparing with galaxy spectroscopic redshifts, photometric redshift dispersion {sigma}({Delta}z/(1+z)) is 0.032 and catastrophic failure rate {Delta}z/(1+z)>0.15 is 5.8% at z<1. Our redshifts are highly accurate with z'<22 at zph<2.5 and for fainter sources with z'<24 at z<1.
We study zCOSMOS-bright optical spectra for 609 Spitzer MIPS 24um-selected galaxies with S_24um_>0.30mJy and I<22.5 (AB mag) over 1.5deg^2^ of the COSMOS field.
We present new images and photometry of the massive star-forming complex Cygnus X obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer for Spitzer (MIPS) on board the Spitzer Space Telescope. A combination of IRAC, MIPS, UKIRT Deep Infrared Sky Survey, and Two Micron All Sky Survey data are used to identify and classify young stellar objects (YSOs). Of the 8231 sources detected exhibiting infrared excess in Cygnus X North, 670 are classified as class I and 7249 are classified as class II. Using spectra from the FAST Spectrograph at the Fred L. Whipple Observatory and Hectospec on the MMT, we spectrally typed 536 sources in the Cygnus X complex to identify the massive stars. We find that YSOs tend to be grouped in the neighborhoods of massive B stars (spectral types B0 to B9).
We study the optical spectral properties of a sample of stars showing far infrared colours similar to those of well-known planetary nebulae. The large majority of them were unidentified sources or poorly known in the literature at the time when this spectroscopic survey started, some 15 years ago. We present low-resolution optical spectroscopy, finding charts and improved astrometric coordinates of a sample of 253 IRAS sources.