• The H II galaxy Hubble diagram strongly favours R-h = ct over Lambda CDM

      Wei, Jun-Jie; Wu, Xue-Feng; Melia, Fulvio; Univ Arizona, Dept Phys; Univ Arizona, Dept Astron (OXFORD UNIV PRESS, 2016-12-01)
      We continue to build support for the proposal to use H II galaxies (HIIGx) and giant extragalactic H II regions (GEHR) as standard candles to construct the Hubble diagram at redshifts beyond the current reach of Type Ia supernovae. Using a sample of 25 high-redshift HIIGx, 107 local HIIGx, and 24 GEHR, we confirm that the correlation between the emission -line luminosity and ionized -gas velocity dispersion is a viable luminosity indicator, and use it to test and compare the standard model Lambda CDM and the R-h = ct universe by optimizing the parameters in each cosmology using a maximization of the likelihood function. For the flat Lambda CDM model, the best fit is obtained with Omega(m) = 0.40(-0.09)(+0.09). However, statistical tools, such as the Akaike (AIC), Kullback (KIC) and Bayes (BIC) Information Criteria favour R-h = Ct over the standard model with a likelihood of approximate to 94.8-98.8 per cent versus only per cent. For wCDM (the version of ACDM with a dark -energy equation of state wde = Pde/Pde rather than was t WA = 1), a statistically acceptable fit is realized with Omega(m) = 0.221(-0.14)(+0.16) and wde = 0.511'0'21-5" which, however, are not fully consistent with their concordance values. In this case, wCDM has two more free parameters than R-h = Ct, and is penalized more heavily by these criteria. We find that R-h = Ct is strongly favoured over wCDM with a likelihood of approximate to 92.9-99.6 per cent versus only 0.4-7.1 per cent. The current HIIGx sample is already large enough for the BIC to rule out ACDM/wCDM in favour of R-h = Ct at a confidence level approaching 3 sigma.
    • The Intricate Structure of HH 508, the Brightest Microjet in the Orion Nebula

      Wu, Ya-Lin; Close, Laird M.; Kim, Jinyoung Serena; Males, Jared R.; Morzinski, Katie M.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-02-21)
      We present Magellan adaptive optics Ha imaging of HH 508, which has the highest surface brightness among protostellar jets in the Orion Nebula. We find that HH 508 actually has a shorter component to the west, and a longer and knotty component to the east. The east component has a kink at 0.'' 3 from the jet-driving star theta(1) Ori B-2, so it may have been deflected by the wind/radiation from the nearby theta(1) Ori B1B5. The origin of both components is unclear, but if each of them is a separate jet, then theta(1) Ori B-2 may be a tight binary. Alternatively, HH 508 may be a slow-moving outflow, and each component represents an illuminated cavity wall. The ionization front surrounding theta(1) Ori B2B3 does not directly face theta(1) Ori B1B5, suggesting that the EUV radiation from theta(1) Ori C plays a dominant role in affecting the morphology of proplyds even in the vicinity of theta(1) Ori B1B5. Finally, we report an Ha blob that might be ejected by the binary proplyd LV 1.
    • The Lifetimes of Phases in High-mass Star-forming Regions

      Battersby, Cara; Bally, John; Svoboda, Brian; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2017-02-01)
      High-mass stars form within star clusters from dense, molecular regions (DMRs), but is the process of cluster formation slow and hydrostatic or quick and dynamic? We link the physical properties of high-mass star-forming regions with their evolutionary stage in a systematic way, using Herschel and Spitzer data. In order to produce a robust estimate of the relative lifetimes of these regions, we compare the fraction of DMRs above a column density associated with high-mass star formation, N(H-2) > 0.4-2.5 x 10(22) cm(-2), in the "starless" (no signature of stars >= 10 M circle dot forming) and star-forming phases in a 2 degrees x 2(degrees) region of the Galactic Plane centered at l = 30 degrees. Of regions capable of forming high-mass stars on similar to 1 pc scales, the starless (or embedded beyond detection) phase occupies about 60%-70% of the DMR lifetime, and the star-forming phase occupies about 30%-40%. These relative lifetimes are robust over a wide range of thresholds. We outline a method by which relative lifetimes can be anchored to absolute lifetimes from large-scale surveys of methanol masers and UCHII regions. A simplistic application of this method estimates the absolute lifetime of the starless phase to be 0.2-1.7 Myr (about 0.6-4.1 fiducial cloud free-fall times) and the star-forming phase to be 0.1-0.7 Myr (about 0.4-2.4 free-fall times), but these are highly uncertain. This work uniquely investigates the star-forming nature of high column density gas pixel by pixel, and our results demonstrate that the majority of high column density gas is in a starless or embedded phase.
    • Locating the intense interstellar scattering towards the inner Galaxy

      Dexter, J.; Deller, A.; Bower, G. C.; Demorest, P.; Kramer, M.; Stappers, B.W.; Lyne, A. G.; Kerr, M.; Spitler, L. G.; Psaltis, D.; et al. (OXFORD UNIV PRESS, 2017-11)
      We use VLBA+VLA observations to measure the sizes of the scatter-broadened images of six of the most heavily scattered known pulsars: three within the Galactic Centre (GC) and three elsewhere in the inner Galactic plane (Delta l < 20 degrees). By combining the measured sizes with temporal pulse broadening data from the literature and using the thin-screen approximation, we locate the scattering medium along the line of sight to these six pulsars. At least two scattering screens are needed to explain the observations of the GC sample. We show that the screen inferred by previous observations of SGR J1745-2900 and Sgr A*, which must be located far from the GC, falls off in strength on scales less than or similar to 0 degrees.2. A second scattering component closer to (Delta < 2 kpc) or even (tentatively) within (Delta < 700 pc) the GC produces most or all of the temporal broadening observed in the other GC pulsars. Outside the GC, the scattering locations for all three pulsars are similar or equal to 2 kpc from Earth, consistent with the distance of the Carina-Sagittarius or Scutum spiral arm. For each object the 3D scattering origin coincides with a known H II region (and in one case also a supernova remnant), suggesting that such objects preferentially cause the intense interstellar scattering seen towards the Galactic plane. We show that the H II regions should contribute greater than or similar to 25 per cent of the total dispersion measure (DM) towards these pulsars, and calculate reduced DM distances. Those distances for other pulsars lying behind H II regions may be similarly overestimated.
    • The PDR structure and kinematics around the compact H ii regions S235 A and S235 C with [C ii], [13C ii], [O i], and HCO+ line profiles

      Kirsanova, M S; Ossenkopf-Okada, V; Anderson, L D; Boley, P A; Bieging, J H; Pavlyuchenkov, Ya N; Luisi, M; Schneider, N; Andersen, M; Samal, M R; et al. (OXFORD UNIV PRESS, 2020-07-30)
      The aim of this work is to study structure and gas kinematics in the photodissociation regions (PDRs) around the compact H II regions S235 A and S235 C. We observe the [C II], [C-13 II], and [O I] line emission, using SOFIA/upGREAT, and complement them by data of HCO+ and CO. We use the [C-13 II] line to measure the optical depth of the [C II] emission, and find that the [C II] line profiles are influenced by self-absorption, while the [C-13 II] line remains unaffected by these effects. Hence, for dense PDRs, [C-13 II] emission is a better tracer of gas kinematics. The optical depth of the [C II] line is up to 10 in S235 A. We find an expanding motion of the [C II]-emitting layer of the PDRs into the front molecular layer in both regions. Comparison of the gas and dust columns shows that gas components visible neither in the [C II] nor in low-J CO lines may contribute to the total column across S235 A. We test whether the observed properties of the PDRs match the predictions of spherical models of expanding H II region + PDR + molecular cloud. Integrated intensities of the [C-13 II], [C II], and [O I] lines are well represented by the model, but the models do not reproduce the double-peaked [C II] line profiles due to an insufficient column density of C+. The model predicts that the [O I] line could be a more reliable tracer of gas kinematics, but the foreground self-absorbing material does not allow using it in the considered regions.
    • Physical properties and H-ionizing-photon production rates of extreme nearby star-forming regions

      Chevallard, Jacopo; Charlot, Stéphane; Senchyna, Peter; Stark, Daniel P; Vidal-García, Alba; Feltre, Anna; Gutkin, Julia; Jones, Tucker; Mainali, Ramesh; Wofford, Aida; et al. (OXFORD UNIV PRESS, 2018-09)
      Measurements of the galaxy UV luminosity function at z greater than or similar to 6 suggest that young stars hosted in low-mass star-forming galaxies produced the bulk of hydrogen-ionizing photons necessary to reionize the intergalactic medium (IGM) by redshift z similar to 6. Whether star-forming galaxies dominated cosmic reionization, however, also depends on their stellar populations and interstellar medium properties, which set, among other things, the production rate of H-ionizing photons,. xi(star)(ion), and the fraction of these escaping into the IGM. Given the difficulty of constraining with existing observatories the physical properties of z greater than or similar to 6 galaxies, in this work we focus on a sample of 10 nearby objects showing UV spectral features comparable to those observed at z greater than or similar to 6. We use the new-generation BEAGLE tool to model the UV-to-optical photometry and UV/optical emission lines of these local 'analogues' of high-redshift galaxies, finding that our relatively simple, yet fully self-consistent, physical model can successfully reproduce the different observables considered. Our galaxies span a broad range of metallicities and are characterized by high ionization parameters, low dust attenuation, and very young stellar populations. Through our analysis, we derive a novel diagnostic of the production rate of H-ionizing photons per unit UV luminosity,. xi(star)(ion), based on the equivalent width of the bright [O III] lambda lambda 4959,5007 line doublet, which does not require measurements of H-recombination lines. This new diagnostic can be used to estimate. xi(star)(ion) from future direct measurements of the [OIII] lambda lambda 4959,5007 line using JWST/NIRSpec (out to z similar to 9.5), and by exploiting the contamination by H, ss + [O III] lambda lambda 4959,5007 of photometric observations of distant galaxies, for instance from existing Spitzer/IRAC data and from future ones with JWST/NIRCam.
    • Probing ISM Structure in Trumpler 14 and Carina I Using the Stratospheric Terahertz Observatory 2

      Seo, Young Min; Goldsmith, Paul F.; Walker, Christopher K.; Hollenbach, David J.; Wolfire, Mark G.; Kulesa, Craig A.; Tolls, Volker; Bernasconi, Pietro N.; Kavak, Ümit; van der Tak, Floris F. S.; et al. (IOP PUBLISHING LTD, 2019-06-20)
      We present observations of the Trumpler 14/Carina I region carried out using the Stratospheric Terahertz Observatory 2. The Trumpler 14/Carina I region is in the western part of the Carina Nebula Complex (CNC), which is one of the most extreme star-forming regions in the Milky Way. We observed Trumpler 14/Carina I in the 58 mu m transition of [C II] with a spatial resolution of 48 '' and a velocity resolution of 0.17 km s(-1). The observations cover a 0 degrees.25 by 0 degrees.28 area with central position l = 297 degrees.34, b = -0 degrees.60. The kinematics show that bright [C II] structures are spatially and spectrally correlated with the surfaces of CO clouds, tracing the photodissociation region (PDR) and ionization front of each molecular cloud. Along seven lines of sight (LOSs) that traverse Tr 14 into the dark ridge to the southwest, we find that the [C II] luminosity from the H II region is 3.7 times that from the PDR. In the same LOS, we find in the PDRs an average ratio of 1 : 4.1 : 5.6 for the mass in atomic gas : dark CO gas : molecular gas traced by CO. Comparing multiple gas tracers, including H I 21 cm, [C II], CO, and radio recombination lines, we find that the H II regions of the CNC are well described as H II regions with one side freely expanding toward us, consistent with the Champagne model of ionized gas evolution. The dispersal of the GMC in this region is dominated by EUV photoevaporation; the dispersal timescale is 20-30 Myr.
    • Proper motions of five OB stars with candidate dusty bow shocks in the Carina Nebula

      Kiminki, Megan M.; Smith, Nathan; Reiter, Megan; Bally, John; Univ Arizona, Steward Observ (OXFORD UNIV PRESS, 2017-06)
      We constrain the proper motions of five OB stars associated with candidate stellar wind bow shocks in the Carina Nebula using Hubble Space Telescope ACS imaging over 9-10 yr baselines. These proper motions allow us to directly compare each star's motion to the orientation of its candidate bow shock. Although these stars are saturated in our imaging, we assess their motion by the shifts required to minimize residuals in their airy rings. The results limit the direction of each star's motion to sectors less than 90 degrees wide. None of the five stars are moving away from the Carina Nebula's central clusters as runaway stars would be, confirming that a candidate bow shock is not necessarily indicative of a runaway star. Two of the five stars are moving tangentially relative to the orientation of their candidate bow shocks, both of which point at the OB cluster Trumpler 14. In these cases, the large-scale flow of the interstellar medium, powered by feedback from the cluster, appears to dominate over the motion of the star in producing the observed candidate bow shock. The remaining three stars all have some component of motion towards the central clusters, meaning that we cannot distinguish whether their candidate bow shocks are indicators of stellar motion, of the flow of ambient gas or of density gradients in their surroundings. In addition, these stars' lack of outward motion hints that the distributed massive-star population in Carina's South Pillars region formed in place, rather than migrating out from the association's central clusters.
    • PROPLYDS AROUND A B1 STAR: 42 ORIONIS IN NGC 1977

      Kim, Jinyoung Serena; Clarke, Cathie J.; Fang, Min; Facchini, Stefano; Univ Arizona, Steward Observ (2016-07-20)
      We present the discovery of seven new proplyds (i.e., sources surrounded by cometary H alpha emission characteristic of offset ionization fronts (IFs)) in NGC 1977, located about 30' north of the Orion Nebula Cluster (ONC) at a distance of similar to 400 pc. Each of these proplyds is situated at projected distances 0.04-0.27 pc from the B1V star 42 Orionis (c Ori), which is the main source of UV photons in the region. In all cases the IFs of the proplyds are clearly pointing toward the common ionizing source, 42 Ori, and six of the seven proplyds clearly show tails pointing away from it. These are the first proplyds to be found around a B star, with previously known examples instead being located around O stars, including those in the ONC around theta(1) Ori C. The radii of the offset IFs in our proplyds are between similar to 200 and 550 au; two objects also contain clearly resolved central sources that we associate with disks of radii 50-70 au. The estimated strength of the FUV radiation field impinging on the proplyds is around 10-30 times less than that incident on the classic proplyds in the ONC. We show that the observed proplyd sizes are however consistent with recent models for FUV photoevaporation in relatively weak FUV radiation fields.