skip to main content


Title: Atomic Shocks in the Outflow of L1551 IRS 5 Identified with SOFIA-upGREAT Observations of [O i]
Abstract We present velocity-resolved Stratospheric Observatory for Infrared Astronomy (SOFIA)/upgrade German REceiver for Astronomy at Terahertz Frequencies observations of [O i ] and [C ii ] lines toward a Class I protostar, L1551 IRS 5, and its outflows. The SOFIA observations detect [O i ] emission toward only the protostar and [C ii ] emission toward the protostar and the redshifted outflow. The [O i ] emission has a width of ∼100 km s −1 only in the blueshifted velocity, suggesting an origin in shocked gas. The [C ii ] lines are narrow, consistent with an origin in a photodissociation region. Differential dust extinction from the envelope due to the inclination of the outflows is the most likely cause of the missing redshifted [O i ] emission. Fitting the [O i ] line profile with two Gaussian components, we find one component at the source velocity with a width of ∼20 km s −1 and another extremely broad component at −30 km s −1 with a width of 87.5 km s −1 , the latter of which has not been seen in L1551 IRS 5. The kinematics of these two components resemble cavity shocks in molecular outflows and spot shocks in jets. Radiative transfer calculations of the [O i ], high- J CO, and H 2 O lines in the cavity shocks indicate that [O i ] dominates the oxygen budget, making up more than 70% of the total gaseous oxygen abundance and suggesting [O]/[H] of ∼1.5 × 10 −4 . Attributing the extremely broad [O i ] component to atomic winds, we estimate an intrinsic mass-loss rate of (1.3 ± 0.8) × 10 −6 M ⊙ yr −1 . The intrinsic mass-loss rates derived from low- J CO, [O i ], and H i are similar, supporting the model of momentum-conserving outflows, where the atomic wind carries most momentum and drives the molecular outflows.  more » « less
Award ID(s):
1910106
NSF-PAR ID:
10334283
Author(s) / Creator(s):
; ; ; ; ; ; ;
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
925
Issue:
1
ISSN:
0004-637X
Page Range / eLocation ID:
93
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract Constraining the physical and chemical structure of young embedded disks is crucial for understanding the earliest stages of planet formation. As part of the Early Planet Formation in Embedded Disks Atacama Large Millimeter/submillimeter Array Large Program, we present high spatial resolution (∼0.″1 or ∼15 au) observations of the 1.3 mm continuum and 13 CO J = 2–1, C 18 O J = 2–1, and SO J N = 6 5 –5 4 molecular lines toward the disk around the Class I protostar L1489 IRS. The continuum emission shows a ring-like structure at 56 au from the central protostar and tenuous, optically thin emission extending beyond ∼300 au. The 13 CO emission traces the warm disk surface, while the C 18 O emission originates from near the disk midplane. The coincidence of the radial emission peak of C 18 O with the dust ring may indicate a gap-ring structure in the gaseous disk as well. The SO emission shows a highly complex distribution, including a compact, prominent component at ≲30 au, which is likely to originate from thermally sublimated SO molecules. The compact SO emission also shows a velocity gradient along a direction tilted slightly (∼15°) with respect to the major axis of the dust disk, which we interpret as an inner warped disk in addition to the warp around ∼200 au suggested by previous work. These warped structures may be formed by a planet or companion with an inclined orbit, or by a gradual change in the angular momentum axis during gas infall. 
    more » « less
  2. ABSTRACT

    NGC 7538 IRS 2 is a compact H ii region and recent star formation source, with a shell morphology, lying on the border of the visible H ii region NGC 7538. We present a spectral cube of the [Ne ii] 12.8 $\mu$m emission line obtained with the TEXES spectrometer on Gemini North with velocity resolution ∼4 km s−1 and angular resolution ∼0.3 arcsec. The kinematics of the data cube show ionized gas flowing along multiple cavity walls. We have simulated the kinematics and structure of IRS 2 with a model of superimposed cavities created by outflows from embedded stars in a cloud with density gradients. Most of the cavities, including the largest that dominates IRS 2 structure, are associated with B-type stars; the outflow of the bright ionizing O star binary IRS 2a/b is small in extent and lies in a high-density clump. The IRS 2 model shows that the behaviour of an H ii region is not a matter of only the most massive star present; cloud clumpiness and activity of lower mass stars may determine the structure and kinematics.

     
    more » « less
  3. ABSTRACT

    The observed properties of the Lyman-α (Ly α) emission line are a powerful probe of neutral gas in and around galaxies. We present spatially resolved Ly α spectroscopy with VLT/MUSE targeting VR7, a UV-luminous galaxy at z = 6.532 with moderate Ly α equivalent width (EW0 ≈ 38 Å). These data are combined with deep resolved [CII]158μm spectroscopy obtained with ALMA and UV imaging from HST and we also detect UV continuum with MUSE. Ly α emission is clearly detected with S/N ≈ 40 and FWHM of 374 km s−1. Ly α and [C ii] are similarly extended beyond the UV, with effective radius reff = 2.1 ± 0.2 kpc for a single exponential model or r$_{\rm eff, Ly\alpha , halo} = 3.45^{+1.08}_{-0.87}$ kpc when measured jointly with the UV continuum. The Ly α profile is broader and redshifted with respect to the [C ii] line (by 213 km s−1), but there are spatial variations that are qualitatively similar in both lines and coincide with resolved UV components. This suggests that the emission originates from two components with plausibly different H i column densities. We place VR7 in the context of other galaxies at similar and lower redshift. The Ly α halo scale length is similar at different redshifts and velocity shifts with respect to the systemic are typically smaller. Overall, we find little indications of a more neutral vicinity at higher redshift. This means that the local (∼10 kpc) neutral gas conditions that determine the observed Ly α properties in VR7 resemble the conditions in post-reionization galaxies.

     
    more » « less
  4. Abstract

    The Makani galaxy hosts the poster child of a galactic wind on scales of the circumgalactic medium. It consists of a two-episode wind in which the slow, outer wind originated 400 Myr ago (Episode I;RI= 20 − 50 kpc) and the fast, inner wind is 7 Myr old (Episode II;RII= 0 − 20 kpc). While this wind contains ionized, neutral, and molecular gas, the physical state and mass of the most extended phase—the warm, ionized gas—are unknown. Here we present Keck optical spectra of the Makani outflow. These allow us to detect hydrogen lines out tor= 30–40 kpc and thus constrain the mass, momentum, and energy in the wind. Many collisionally excited lines are detected throughout the wind, and their line ratios are consistent with 200–400 km s−1shocks that power the ionized gas, withvshock=σwind. Combining shock models, density-sensitive line ratios, and mass and velocity measurements, we estimate that the ionized mass and outflow rate in the Episode II wind could be as high as those of the molecular gas:MIIHIIMIIH2=(12)×109ManddM/dtIIHIIdM/dtIIH2=170250Myr−1. The outer wind has slowed, so thatdM/dtIHII10Myr−1, but it contains more ionized gas,MIHII=5×109M. The momentum and energy in the recent Episode II wind imply a momentum-driven flow (p“boost” ∼7) driven by the hot ejecta and radiation pressure from the Eddington-limited, compact starburst. Much of the energy and momentum in the older Episode I wind may reside in a hotter phase, or lie further into the circumgalactic medium.

     
    more » « less
  5. Abstract

    M82 is an archetypal starburst galaxy in the local Universe. The central burst of star formation, thought to be triggered by M82's interaction with other members in the M81 group, is driving a multiphase galaxy-scale wind away from the plane of the disk that has been studied across the electromagnetic spectrum. Here, we present new velocity-resolved observations of the [Cii] 158μm line in the central disk and the southern outflow of M82 using the upGREAT instrument on board SOFIA. We also report the first detections of velocity-resolved (ΔV= 10 km s−1) [Cii] emission in the outflow of M82 at projected distances of ≈1–2 kpc south of the galaxy center. We compare the [Cii] line profiles to observations of CO and Hiand find that likely the majority (>55%) of the [Cii] emission in the outflow is associated with the neutral atomic medium. We find that the fraction of [Cii] actually outflowing from M82 is small compared to the bulk gas outside the midplane (which may be in a halo or tidal streamers), which has important implications for observations of [Cii] outflows at higher redshift. Finally, by comparing the observed ratio of the [Cii] and CO intensities to models of photodissociation regions, we estimate that the far-ultraviolet (FUV) radiation field in the disk is ∼103.5G0, in agreement with previous estimates. In the outflow, however, the FUV radiation field is 2–3 orders of magnitudes lower, which may explain the high fraction of [Cii] arising from the neutral medium in the wind.

     
    more » « less