Abstract
We present SOFIA observations with HAWC+ and FIFI-LS of the peculiar galaxy Arp 25, also known as NGC 2276 or UGC 3740, whose morphology is deformed by its impact with the intragroup medium ...of the NGC 2300 galaxy group. These observations show the first direct proof of the enhancement of C
ii
emission due to shocks caused by ram pressure in a group of galaxies. By comparing the C
ii
emission to UV attenuation, dust emission, PAH, and CO emission in different regions of the galaxy, we find a clear excess of C
ii
emission along the impact front with the intragroup medium. We estimate that the shock due to the impact with the intragroup medium increases the C
ii
emission along the shock front by 60% and the global C
ii
emission by approximately 25% with respect to the predicted C
ii
emission assuming only excitation caused by stellar radiation. This result shows the danger of interpreting C
ii
emission as directly related to star formation since shocks and other mechanisms can significantly contribute to the total C
ii
emission from galaxies in groups and clusters.
The CO-dark molecular gas mass in 30 Doradus Chevance, Mélanie; Madden, Suzanne C; Fischer, Christian ...
Monthly Notices of the Royal Astronomical Society,
06/2020, Letnik:
494, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Determining the efficiency with which gas is converted into stars in galaxies requires an accurate determination of the total reservoir of molecular gas mass. However, despite being the most ...abundant molecule in the Universe, H2 is challenging to detect through direct observations and indirect methods have to be used to estimate the total molecular gas reservoir. These are often based on scaling relations from tracers such as CO or dust, and are generally calibrated in the Milky Way. Yet, evidence that these scaling relations are environmentally dependent is growing. In particular, the commonly used CO-to-H2 conversion factor (XCO) is expected to be higher in metal-poor and/or strongly UV-irradiated environments. We use new SOFIA/FIFI-LS observations of far-infrared fine-structure lines from the ionized and neutral gas and the Meudon photodissociation region model to constrain the physical properties and the structure of the gas in the massive star-forming region of 30 Doradus in the Large Magellanic Cloud, and determine the spatially resolved distribution of the total reservoir of molecular gas in the proximity of the young massive cluster R136. We compare this value with the molecular gas mass inferred from ground-based CO observations and dust-based estimates to quantify the impact of this extreme environment on commonly used tracers of the molecular gas. We find that the strong radiation field combined with the half-solar metallicity of the surrounding gas is responsible for a large reservoir of ‘CO-dark’ molecular gas, leaving a large fraction of the total H2 gas (≳75 per cent) undetected when adopting a standard XCO factor in this massive star-forming region.
We introduce a new infrared diagnostic to separate galaxies on the basis of their dominant infrared emission: stellar or nuclear. The main novelty with respect to existing diagnostics is the use of a ...broad band encompassing at the same time the 9.7-μm silicate absorption feature and one of the adjacent broad polycyclic aromatic hydrocarbon (PAH) features. This provides a robust estimate of the near- to mid-infrared continuum slope and enables a clear distinction among different classes of galaxies up to a redshift z ∼ 2.5. The diagnostic can be applied to a wealth of archival data from the ISO, Spitzer and Akari surveys, as well as future James Webb Space Telescope surveys. Based on data in the Great Observatories Origins Deep Survey (GOODS), Lockman Hole and North Ecliptic Pole fields, we find that approximately 70 per cent of active galactic nuclei (AGNs) detected with X-ray and optical spectroscopy dominate the total mid-infrared emission. Finally, we estimate that AGNs contribute less than 30 per cent of the mid-infrared extragalactic integrated emission.
Abstract
We present the characterization and definitive flux calibration of the Far-infrared Field Integral Line Spectrometer (FIFI-LS) instrument on board SOFIA. The work is based on measurements ...made in the laboratory with an internal calibrator and on observations of planets, moons, and asteroids as absolute flux calibrators made during the entire lifetime of the instrument. We describe the techniques used to derive flat fields, water vapor column estimates, detector linearity, spectral and spatial resolutions, and absolute flux calibration. Two sets of responses are presented, before and after the entrance filter window was changed in 2018 to improve the sensitivity at 52
μ
m, a wavelength range previously not covered by PACS on Herschel. The relative spectral response of each detector and the illumination pattern of the arrays of the FIFI-LS arrays are derived using the internal calibrator before each observational series. The linearity of the array response is estimated by considering observations of bright sources. We find that the deviation from the linearity of the FIFI-LS arrays affects the flux estimations by less than 1%. The flux calibration accuracy is estimated to be 15% or better across the entire wavelength range of the instrument. The limited availability of sky calibrators during each observational series is the major limiting factor of the flux calibration accuracy.
Abstract
To understand star formation rates, studying feedback mechanisms that regulate star formation is necessary. The radiation emitted by nascent massive stars play a significant role in feedback ...by photodissociating and ionizing their parental molecular clouds. To gain a detailed picture of the physical processes, we mapped the photodissociation region (PDR) M17-SW in several fine-structure and high-
J
CO lines with FIFI-LS, the far-infrared imaging spectrometer aboard SOFIA. An analysis of the CO and O
i
146
μ
m line intensities, combined with the far-infrared intensity, allows us to create a density and UV intensity map using a one-dimensional model. The density map reveals a sudden change in the gas density crossing the PDR. The strengths and limits of the model and the locations of the ionization and photodissociation front of the edge-on PDR are discussed.
Abstract
We present integral field, far-infrared (FIR) spectroscopy of Mrk 54, a local Lyman continuum emitter, obtained with FIFI-LS on the Stratospheric Observatory for Infrared Astronomy. This is ...only the second time, after Haro 11, that C
ii
158
μ
m and O
iii
88
μ
m spectroscopy of the known LCEs have been obtained. We find that Mrk 54 has a strong C
ii
emission that accounts for ∼1% of the total FIR luminosity, whereas it has only moderate O
iii
emission, resulting in the low O
iii
/C
ii
luminosity ratio of 0.22 ± 0.06. In order to investigate whether O
iii
/C
ii
is a useful tracer of
f
esc
(LyC escape fraction), we examine the correlations of O
iii
/C
ii
and (i) the optical line ratio of O
32
≡ O
iii
5007 Å/O
ii
3727 Å, (ii) specific star formation rate, (iii) O
iii
88
μ
m/O
i
63
μ
m ratio, (iv) gas-phase metallicity, and (v) dust temperature based on a combined sample of Mrk 54 and the literature data from the Herschel Dwarf Galaxy Survey and the LITTLE THINGS Survey. We find that galaxies with high O
iii
/C
ii
luminosity ratios could be the result of high ionization (traced by O
32
), bursty star formation, high ionized-to-neutral gas volume filling factors (traced by O
iii
88
μ
m/O
i
63
μ
m), and low gas-phase metallicities, which is in agreement with theoretical predictions. We present an empirical relation between the O
iii
/C
ii
ratio and
f
esc
based on the combination of the O
iii
/C
ii
and O
32
correlation, and the known relation between O
32
and
f
esc
. The relation implies that high-redshift galaxies with high O
iii
/C
ii
ratios revealed by the Atacama Large Millimeter/submillimeter Array may have
f
esc
≳ 0.1, significantly contributing to the cosmic reionization.
Context. We present a study of star formation and central black hole accretion activity of galaxies that are hosted in the two nearby (z ~ 0.2) rich galaxy clusters Abell 983 and 1731. Aims. We aim ...to quantify both the obscured and unobscured star formation rates, as well as the presence of active galactic nuclei (AGN) as a function of the environment in which the galaxy is located. Methods. We targeted the clusters with unprecedented deep infrared Spitzer observations (0.2 mJy at 24 micron), near-IR Palomar imaging and optical WIYN spectroscopy. The extent of our observations (~3 virial radii) covers the vast range of possible environments, from the very dense cluster centre to the very rarefied cluster outskirts and accretion regions. Results. The star-forming members of the two clusters present star formation rates that are comparable with those measured in coeval field galaxies. Analysis of the spatial arrangement of the spectroscopically confirmed members reveals an elongated distribution for A1731 with respect to the more uniform distribution of A983. The emerging picture is compatible with A983 being a fully evolved cluster, in contrast with the still actively accreting A1731. Conclusions. Analysis of the specific star formation rate reveals evidence of ongoing galaxy pre-processing along A1731’s filament-like structure. Furthermore, the decrease in the number of star-forming galaxies and AGN towards the cluster cores suggests that the cluster environment is accelerating the ageing process of the galaxies and blocking further accretion of the cold gas that fuels both star formation and black hole accretion activity.
Abstract
We present the C
ii
157.7
μ
m map of galaxy NGC 7331 obtained with the Field-Imaging Far-Infrared Line Spectrometer on board the Stratospheric Observatory for Infrared Astronomy (SOFIA). ...This map extends an existent Herschel/Photodetector Array Camera and Spectrometer observation of the central strip of the galaxy to encompass the entire molecular ring and much of the disk, including multiple spiral arms with intense far-IR emission. We also present Herschel archival data of the N
ii
205
μ
m line, which covers a substantial part of the C
ii
SOFIA observations and allows us to estimate the neutral fraction of the C
ii
emission along the ring and disk of the galaxy. We find that the neutral fraction rises with the distance from the center. In addition, by tracing the azimuthal variation of the neutral fraction, we are able to see how our observing perspective affects this measurement. The high inclination of NGC 7331 allows us to glimpse the internal walls of the molecular ring. There, young bright stars emit UV radiation causing more C
ii
emission to be produced in the ionized gas. On the outer walls, opaque dust shrouds the rest of the ring, making the neutral medium the dominant source of C
ii
emission. Through spatial analysis comparing the C
ii
emission to tracers of gas heating, we are able to investigate how the photoelectric heating efficiency varies throughout NGC 7331 and extend global measurements of the C
ii
deficit to local environments. Since the origin of C
ii
emission has typically been studied in face-on galaxies, our results shed a new light on the interpretation of C
ii
emission, especially when studying distant galaxies with unknown inclination.
Abstract
We report NASA-DLR SOFIA upGREAT circumstellar O
i
63.2
μ
m and C
ii
157.7
μ
m emission profiles and FIFI-LS O
i
63.2
μ
m, O
i
145.5
μ
m, and C
ii
157.7
μ
m fluxes obtained shortly ...after Betelgeuse’s 2019/2020 Great Dimming event. Haas et al. noted a potential correlation between the O
i
63.2
μ
m flux and
V
magnitude based on three Kuiper Airborne Observatory observations made with the CGS and FIFI instruments. The FIFI observation was obtained when V ≃ 0.88 and revealed a 3
σ
non-detection at a quarter of the previous CGS flux measurement made when
V
≃ 0.35. A potential explanation could be a change in dust-gas drag heating by circumstellar silicates caused by variations in the photospheric radiation field. SOFIA observations provide a unique test of this correlation because the
V
-band brightness went to its lowest value on record,
V
≃ 1.61, with the SOFIA observations being made when
V
FIFI−LS
≃ 1.51 and
V
upGREAT
≃ 1.36. The upGREAT spectra show a O
i
63.2
μ
m flux larger than previous space observatory measurements obtained when
V
≃ 0.58. The profile is consistent with formation in the slower, more turbulent inner S1 outflow, while the C
ii
157.7
μ
m profile is consistent with formation farther out in the faster S2 outflow. Modeling of dust-gas drag heating, combined with 25 yr of Wing three-filter and
V
photometry, reveals that it is unlikely that the S1 circumstellar envelope and O
i
63.2
μ
m fluxes are dominated by the dust-gas drag heating and that another heating source is also active. The O
i
63.2
μ
m profile is hard to reconcile with existing outflow velocity models.
Abstract
We present Herschel, ALMA, and MUSE observations of the molecular ring of Messier 104, also known as the Sombrero galaxy. These previously unpublished archival data shed new light on the ...content of the interstellar medium of M104. In particular, molecular hydrogen measured by CO emission and dust measured by far-infrared light are uniformly distributed along the ring. The ionized gas revealed by H
α
and C
ii
emission is distributed in knots along the ring. Despite being classified as an SAa galaxy, M104 displays features typical of early-type galaxies. We therefore compared its C
ii
and dust emission to a sample of early-type galaxies observed with Herschel and SOFIA. The C
ii
/FIR ratio of M104 is much lower than that of typical star-forming galaxies and is instead much more similar to that of early-type galaxies. By classifying regions using optical emission line diagnostics, we also find that regions classified as H
ii
lie closer to star-forming galaxies in the C
ii
/FIR diagram than those classified as low-ionization emission regions. The good match between C
ii
and H
α
emission, in conjunction with the lack of correlation between CO emission and star formation, suggests that there is very limited active star formation along the ring and that most of the C
ii
emission is from ionized and neutral atomic gas rather than molecular gas. From the total intensity of the CO line, we estimate a molecular hydrogen mass of 0.9 × 10
9
M
⊙
, a value intermediate between those of early-type galaxies and the content of the molecular ring of our galaxy.
![Shock Enhanced [C ii] Emiss...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X_1538-4357/small "Shock Enhanced [C ii] Emission from the Infalling Galaxy Arp 25")
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