3,416 research outputs found

    The Star Formation Across Cosmic Time (SFACT) Survey. I. Survey Description and Early Results from a New Narrow-Band Emission-Line Galaxy Survey

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    We introduce the Star Formation Across Cosmic Time (SFACT) survey. SFACT is a new narrow-band survey for emission-line galaxies (ELGs) and QSOs being carried out using the wide-field imager on the WIYN 3.5 m telescope. Because of the superior depth and excellent image quality afforded by WIYN, we routinely detect ELGs to r = 25.0. Our survey observations are made using three custom narrow-band filters centered on 6590 A, 6950 A, and 7460 A. Due to the sensitivity of the survey, we are able to simultaneously detect sources via a number of different emission lines over a wide range of redshifts. The principal lines detected in SFACT are H-alpha (redshifts up to 0.144), [O III]5007 (redshifts up to 0.500) and [O II]3727 (redshifts up to 1.015). In this paper we detail the properties of the survey as well as present initial results obtained by analyzing our three pilot-study fields. These fields have yielded a total of 533 ELG candidates in an area of 1.50 square degrees (surface density of 355 ELGs per square degree). Follow-up spectra for a subset of the ELG candidates are also presented. One of the key attributes of the SFACT survey is that the ELGs are detected in discrete redshift windows that will allow us to robustly quantify the properties of the star-forming and AGN populations as a function of redshift to z = 1 and beyond. The planned acquisition of additional narrow-band filters will allow us to expand our survey to substantially higher redshifts.Comment: 27 pages, 13 figures. Accepted for publication in the Astronomical Journa

    Discovery of a Gas-Rich Companion to the Extremely Metal-Poor Galaxy DDO 68

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    We present HI spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only 3% Z_{\odot}, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of the chemical evolution of galaxies. One possible solution to this problem is the infall of pristine neutral gas, potentially initiated during a gravitational interaction. Using archival HI spectral-line imaging obtained with the Karl G. Jansky Very Large Array, we have discovered a previously unknown companion of DDO 68. This low-mass (MHI_{\rm HI} == 2.8×\times107^{7} M_{\odot}), recently star-forming (SFRFUV_{\rm FUV} == 1.4×\times103^{-3} M_{\odot} yr1^{-1}, SFRHα_{\rm H\alpha} << 7×\times105^{-5} M_{\odot} yr1^{-1}) companion has the same systemic velocity as DDO 68 (Vsys_{\rm sys} == 506 km s1^{-1}; D == 12.74±\pm0.27 Mpc) and is located at a projected distance of 42 kpc. New HI maps obtained with the 100m Robert C. Byrd Green Bank Telescope provide evidence that DDO 68 and this companion are gravitationally interacting at the present time. Low surface brightness HI gas forms a bridge between these objects.Comment: Accepted for publication in the Astrophysical Journal Letter

    Investigating the Cosmic-Ray Ionization Rate Near the Supernova Remnant IC 443 Through H3+ Observations

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    Observational and theoretical evidence suggests that high-energy Galactic cosmic rays are primarily accelerated by supernova remnants. If also true for low-energy cosmic rays, the ionization rate near a supernova remnant should be higher than in the general Galactic interstellar medium (ISM). We have searched for H3+ absorption features in 6 sight lines which pass through molecular material near IC 443---a well-studied case of a supernova remnant interacting with its surrounding molecular material---for the purpose of inferring the cosmic-ray ionization rate in the region. In 2 of the sight lines (toward ALS 8828 and HD 254577) we find large H3+ column densities, N(H3+)~3*10^14 cm^-2, and deduce ionization rates of zeta_2~2*10^-15 s^-1, about 5 times larger than inferred toward average diffuse molecular cloud sight lines. However, the 3 sigma upper limits found for the other 4 sight lines are consistent with typical Galactic values. This wide range of ionization rates is likely the result of particle acceleration and propagation effects, which predict that the cosmic-ray spectrum and thus ionization rate should vary in and around the remnant. While we cannot determine if the H3+ absorption arises in post-shock (interior) or pre-shock (exterior) gas, the large inferred ionization rates suggest that IC 443 is in fact accelerating a large population of low-energy cosmic rays. Still, it is unclear whether this population can propagate far enough into the ISM to account for the ionization rate inferred in diffuse Galactic sight lines.Comment: 14 pages, 3 figures, 4 table

    A JWST/MIRI and NIRCam Analysis of the Young Stellar Object Population in the Spitzer I region of NGC 6822

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    We present an imaging survey of the Spitzer~I star-forming region in NGC 6822 conducted with the NIRCam and MIRI instruments onboard JWST. Located at a distance of 490 kpc, NGC 6822 is the nearest non-interacting low-metallicity (\sim0.2 ZZ_{\odot}) dwarf galaxy. It hosts some of the brightest known HII regions in the local universe, including recently discovered sites of highly-embedded active star formation. Of these, Spitzer I is the youngest and most active, and houses 90 color-selected candidate young stellar objects (YSOs) identified from Spitzer Space Telescope observations. We revisit the YSO population of Spitzer~I with these new JWST observations. By analyzing color-magnitude diagrams (CMDs) constructed with NIRCam and MIRI data, we establish color selection criteria and construct spectral energy distributions (SEDs) to identify candidate YSOs and characterize the full population of young stars, from the most embedded phase to the more evolved stages. In this way, we have identified 129 YSOs in Spitzer I. Comparing to previous Spitzer studies of the NGC 6822 YSO population, we find that the YSOs we identify are fainter and less massive, indicating that the improved resolution of JWST allows us to resolve previously blended sources into individual stars.Comment: 17 pages, 9 figures, 2 tables, to be submitted to ApJ, comments welcom

    Dissecting the Mid-Infrared Heart of M83 with JWST

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    We present a first look at the MRS observations of the nucleus of the spiral galaxy M83, taken with MIRI onboard JWST. The observations show a rich set of emission features from the ionized and warm molecular gas, as well as traces of the dust properties in this highly star forming environment. To begin dissecting the complex processes taking place in this part of the galaxy, we divide the nucleus observations into four different regions. We find that the strength of the emission features appears to strongly vary in all four regions, with the south-east region displaying the weakest features tracing both the dust continuum and ISM properties. Comparison between the cold molecular gas traced by the 12^{12}CO (1-0) transition with ALMA and the H2_2 0-0 S(1) transition showed a similar spatial distribution throughout the nucleus. This is in contrast to the distribution of the much warmer H2_2 emission from the S(7) transition found to be concentrated mainly around the optical nucleus. We modeled the H2_2 excitation using the rotational emission lines and estimate a total molecular gas mass accounting for the warm H2_2 component of M(>>50 K)H2_{\rm H_{2}} = 59.33 (±4.75\pm 4.75) ×\times 106^{6} M_{\odot}. We compared this value to the total molecular gas mass inferred by probing the cold H2_2 gas through the 12^{12}CO (1-0) emission, M(CO)H2_{\rm H_{2}} = 14.99 ×\times 106^{6} M_{\odot}. Our findings indicate that \sim75\% of the total molecular gas mass in the core of M83 is contained in the warm H2_2 component. We also identify [OIV]25.89 μ\mum and [FeII]25.99 μ\mum emission (indicative of shocks) in all four nuclear regions with the strongest emission originating from the north-west section. We propose that the diffuse [FeII]25.99 μ\mum emission is an indication of the combined effects of both the collective supernova explosions and the starbursts themselves.Comment: 13 pages, 3 Tables, 8 Figures, to be submitted to Ap
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