56 research outputs found
Revisiting the Temperature of the Diffuse ISM with CHESS Sounding Rocket Observations
Measuring the temperature and abundance patterns of clouds in the
interstellar medium (ISM) provides an observational basis for models of the
physical conditions within the clouds, which play an important role in studies
of star and planet formation. The Colorado High-resolution Echelle Stellar
Spectrograph (CHESS) is a far ultraviolet rocket-borne instrument designed to
study the atomic-to-molecular transitions within diffuse molecular and
translucent cloud regions. The final two flights of the instrument observed
Scorpii ( Sco) and Arae. We present flight results
of interstellar molecular hydrogen (H) excitation on the sightlines,
including measurements of the column densities and temperatures. These results
are compared to previous values that were measured using the damping wings of
low J H absorption features (Savage et al. 1977).
For Sco, we find that the derived column density of the J = 1 rotational level differs by a factor of 2-3 when compared to the
previous observations. We discuss the discrepancies between the two
measurements and show that the source of the difference is due to the opacity
of higher rotational levels contributing to the J = 1
absorption wing, increasing the inferred column density in the previous work.
We extend this analysis to 9 and 13 spectra to explore the
interdependence of the column densities of different rotational levels and how
the H kinetic temperature is influenced by these relationships. We
find a revised average gas kinetic temperature of the diffuse molecular ISM of
T = 68 13 K, 12% lower than the value found previously.Comment: 20 pages, 10 Figures, Accepted in Ap
The Orion Fingers: H_2 Temperatures and Excitation in an Explosive Outflow
We measure H_2 temperatures and column densities across the Orion Becklin-Neugebauer/Kleinmann-Low (BN/KL) explosive outflow from a set of 13 near-infrared (IR) H_2 rovibrational emission lines observed with the TripleSpec spectrograph on Apache Point Observatory's 3.5 m telescope. We find that most of the region is well characterized by a single temperature (~2000–2500 K), which may be influenced by the limited range of upper-energy levels (6000–20,000 K) probed by our data set. The H_2 column density maps indicate that warm H2 comprises 10^(-5)–10^(−3) of the total H_2 column density near the center of the outflow. Combining column density measurements for co-spatial H_2 and CO at T = 2500 K, we measure a CO/H2 fractional abundance of 2 × 10^(−3) and discuss possible reasons why this value is in excess of the canonical 10^(−4) value, including dust attenuation, incorrect assumptions on co-spatiality of the H_2 and CO emission, and chemical processing in an extreme environment. We model the radiative transfer of H_2 in this region with ultraviolet (UV) pumping models to look for signatures of H_2 fluorescence from H i Lyα pumping. Dissociative (J-type) shocks and nebular emission from the foreground Orion H ii region are considered as possible Lyα sources. From our radiative transfer models, we predict that signatures of Lyα pumping should be detectable in near-IR line ratios given a sufficiently strong source, but such a source is not present in the BN/KL outflow. The data are consistent with shocks as the H_2 heating source
The FLASHES Survey I: Integral Field Spectroscopy of the CGM around 48 QSOs
We present the pilot study component of the Fluorescent Lyman-Alpha
Structures in High-z Environments (FLASHES) Survey; the largest integral-field
spectroscopy survey to date of the circumgalactic medium at . We
observed 48 quasar fields between 2015 and 2018 with the Palomar Cosmic Web
Imager (Matuszewski et al. 2010). Extended HI Lyman- emission
is discovered around 42/48 of the observed quasars, ranging in projected,
flux-weighted radius from 21-71 proper kiloparsecs (pkpc), with 26 nebulae
exceeding in effective diameter. The circularly averaged
surface brightness radial profile peaks at a maximum of
( adjusted for
cosmological dimming) and luminosities range from
to
. The emission appears to have a highly
eccentric morphology and a maximum covering factor of ( for giant
nebulae). On average, the nebular spectra are red-shifted with respect to both
the systemic redshift and Ly peak of the quasar spectrum. The
integrated spectra of the nebulae mostly have single or double-peaked line
shapes with global dispersions ranging from to
, though the individual (Gaussian) components of lines
with complex shapes mostly appear to have dispersions
, and the flux-weighted velocity centroids of the lines
vary by thousands of with respect to the systemic QSO
redshifts. Finally, the root-mean-square velocities of the nebulae are found to
be consistent with gravitational motions expected in dark matter halos of mass
. We compare these results to existing
surveys at both higher and lower redshift
Probing UV-sensitive Pathways for CN and HCN Formation in Protoplanetary Disks with the Hubble Space Telescope
The UV radiation field is a critical regulator of gas-phase chemistry in surface layers of disks around young stars. In an effort to understand the relationship between photocatalyzing UV radiation fields and gas emission observed at infrared and submillimeter wavelengths, we present an analysis of new and archival Hubble Space Telescope (HST), Spitzer, ALMA, IRAM, and SMA data for five targets in the Lupus cloud complex and 14 systems in Taurus-Auriga. The HST spectra were used to measure Lyα and far-UV (FUV) continuum fluxes reaching the disk surface, which are responsible for dissociating relevant molecular species (e.g., HCN, N₂). Semi-forbidden C II] λ2325 and UV-fluorescent H₂ emission were also measured to constrain inner disk populations of C⁺ and vibrationally excited H2. We find a significant positive correlation between 14 μm HCN emission and fluxes from the FUV continuum and C II] λ2325, consistent with model predictions requiring N₂ photodissociation and carbon ionization to trigger the main CN/HCN formation pathways. We also report significant negative correlations between submillimeter CN emission and both C II] and FUV continuum fluxes, implying that CN is also more readily dissociated in disks with stronger FUV irradiation. No clear relationships are detected between either CN or HCN and Lyα or UV-H₂ emission. This is attributed to the spatial stratification of the various molecular species, which span several vertical layers and radii across the inner and outer disk. We expect that future observations with the James Webb Space Telescope will build on this work by enabling more sensitive IR surveys than were possible with Spitzer
CHESS: An innovative concept for high-resolution, far-UV spectroscopy
The space ultraviolet (UV) is a critical astronomical observing window, where a multitude of atomic, ionic, and molecular signatures provide crucial insight into planetary, interstellar, stellar, intergalactic, and extragalactic objects. The next generation of large space telescopes require highly sensitive, moderate-to-high resolution UV spectrograph. However, sensitive observations in the UV are difficult, as UV optical performance and imaging efficiencies have lagged behind counterparts in the visible and infrared regimes. This has historically resulted in simple, low-bounce instruments to increase sensitivity. In this study, we present the design, fabrication, and calibration of a simple, high resolution, high throughput FUV spectrograph - the Colorado High-resolution Echelle Stellar Spectrograph (CHESS). CHESS is a sounding rocket payload to demonstrate the instrument design for the next-generation UV space telescopes. We present tests and results on the performance of several state-of-the-art diffraction grating and detector technologies for FUV astronomical applications that were flown aboard the first two iterations of CHESS. The CHESS spectrograph was used to study the atomic-to-molecular transitions within translucent cloud regions in the interstellar medium (ISM) through absorption spectroscopy. The first two flights looked at the sightlines towards α Virgo an
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