Engineering topics

Weiss, A

Publications and source records attributed to Weiss, A.

8 records

DOE OSTI2013

EVIDENCE FOR CO SHOCK EXCITATION IN NGC 6240 FROM HERSCHEL SPIRE SPECTROSCOPY

We present Herschel SPIRE FTS spectroscopy of the nearby luminous infrared galaxy NGC 6240. In total 20 lines are detected, including CO J = 4 - 3 through J = 13 - 12, 6 H{sub 2}O rotational lines, and [C I] and [N II] fine-structure lines. The CO to continuum luminosity ratio is 10 times higher in NGC 6240 than Mrk 231. Although the CO ladders of NGC 6240 and Mrk 231 are very similar, UV and/or X-ray irradiation are unlikely to be responsible for the excitation of the gas in NGC 6240. We applied both C and J shock models to the H{sub 2} v = 1-0 S(1) and v = 2-1 S(1) lines and the CO rotational ladder. The CO ladder is best reproduced by a model with shock velocity v{sub s} = 10 km s{sup -1} and a pre-shock density n{sub H} = 5 Multiplication-Sign 10{sup 4} cm{sup -3}. We find that the solution best fitting the H{sub 2} lines is degenerate. The shock velocities and number densities range between v{sub s} = 17-47 km s{sup -1} and n{sub H} = 10{sup 7}-5 Multiplication-Sign 10{sup 4} cm{sup -3}, respectively. The H{sub 2} lines thus need a much more powerful shock than the CO lines. We deduce that most of the gas is currently moderately stirred up by slow (10 km s{sup -1}) shocks while only a small fraction ({approx}< 1%) of the interstellar medium is exposed to the high-velocity shocks. This implies that the gas is rapidly losing its highly turbulent motions. We argue that a high CO line-to-continuum ratio is a key diagnostic for the presence of shocks.

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DOE OSTI2012

ON THE VARIATIONS OF FUNDAMENTAL CONSTANTS AND ACTIVE GALACTIC NUCLEUS FEEDBACK IN THE QUASI-STELLAR OBJECT HOST GALAXY RXJ0911.4+0551 at z = 2.79

We report on sensitive observations of the CO(J = 7{yields}6) and C I({sup 3}P{sub 2} {yields} {sup 3}P{sub 1}) transitions in the z = 2.79 QSO host galaxy RXJ0911.4+0551 using the IRAM Plateau de Bure interferometer. Our extremely high signal-to-noise spectra combined with the narrow CO line width of this source (FWHM = 120 km s{sup -1}) allows us to estimate sensitive limits on the spacetime variations of the fundamental constants using two emission lines. Our observations show that the C I and CO line shapes are in good agreement with each other but that the C I line profile is of the order of 10% narrower, presumably due to the lower opacity in the latter line. Both lines show faint wings with velocities up to {+-}250 km s{sup -1}, indicative of a molecular outflow. As such, the data provide direct evidence for negative feedback in the molecular gas phase at high redshift. Our observations allow us to determine the observed frequencies of both transitions with so far unmatched accuracy at high redshift. The redshift difference between the CO and C I lines is sensitive to variations of {Delta}F/F with F = {alpha}{sup 2}/{mu} where {alpha} is the fine structure constant and {mu} is the electron-to-proton mass ratio. We find {Delta}F/F (6.9 {+-} 3.7) Multiplication-Sign 10{sup -6} at a look-back time of 11.3 Gyr, which, within the uncertainties, is consistent with no variations of the fundamental constants.

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DOE OSTI2012

EVIDENCE FOR LOW EXTINCTION IN ACTIVELY STAR-FORMING GALAXIES AT z > 6.5

We present a search for the [C II] 158 {mu}m fine structure line (a main cooling line of the interstellar medium) and the underlying far-infrared (FIR) continuum in three high-redshift (6.6 < z < 8.2) star-forming galaxies using the IRAM Plateau de Bure Interferometer. We targeted two Ly{alpha}-selected galaxies (Ly{alpha} emitters, LAEs) with moderate UV-based star formation rates (SFRs {approx} 20 M{sub Sun} yr{sup -1}; Himiko at z = 6.6 and IOK-1 at z = 7.0) and a gamma-ray burst (GRB) host galaxy (GRB 090423 at z {approx} 8.2). Based on our 3{sigma} rest-frame FIR continuum limits, previous (rest-frame) UV continuum measurements and spectral energy distribution (SED) fitting, we rule out SED shapes similar to highly obscured galaxies (e.g., Arp 220, M 82) and less extreme dust-rich nearby spiral galaxies (e.g., M 51) for the LAEs. Conservatively assuming an SED shape typical of local spiral galaxies we derive upper limits for the FIR-based star formation rates (SFRs) of {approx}70 M{sub Sun} yr{sup -1}, {approx}50 M{sub Sun} yr{sup -1}, and {approx}40 M{sub Sun} yr{sup -1} for Himiko, IOK-1, and GRB 090423, respectively. For the LAEs these limits are only a factor {approx}3 higher than the published UV-based SFRs (uncorrected for extinction). This indicates that the dust obscuration in the z > 6 LAEs studied here is lower by a factor of a few than what has recently been found in some LAEs at lower redshift (2 < z < 3.5) with similar UV-based SFRs. A low obscuration in our z > 6 LAE sample is consistent with recent rest-frame UV studies of z {approx} 7 Lyman break galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

IONIZED NITROGEN AT HIGH REDSHIFT

We present secure [N II]{sub 205{mu}m} detections in two millimeter-bright, strongly lensed objects at high redshift, APM 08279+5255 (z = 3.911) and MM 18423+5938 (z = 3.930), using the IRAM Plateau de Bure Interferometer. Due to its ionization energy [N II]{sub 205{mu}m} is a good tracer of the ionized gas phase in the interstellar medium. The measured fluxes are S([N II]{sub 205{mu}m}) = (4.8 {+-} 0.8) Jy km s{sup -1} and (7.4 {+-} 0.5) Jy km s{sup -1}, respectively, yielding line luminosities of L([N II]{sub 205{mu}m}) = (1.8 {+-} 0.3) Multiplication-Sign 10{sup 9} {mu}{sup -1} L{sub Sun} for APM 08279+5255 and L([N II]{sub 205{mu}m}) = (2.8 {+-} 0.2) Multiplication-Sign 10{sup 9} {mu}{sup -1} L{sub Sun} for MM 18423+5938. Our high-resolution map of the [N II]{sub 205{mu}m} and 1 mm continuum emission in MM 18423+5938 clearly resolves an Einstein ring in this source and reveals a velocity gradient in the dynamics of the ionized gas. A comparison of these maps with high-resolution EVLA CO observations enables us to perform the first spatially resolved study of the dust continuum-to-molecular gas surface brightness ({Sigma}{sub FIR}{proportional_to}{Sigma}{sup N}{sub CO}, which can be interpreted as the star formation law) in a high-redshift object. We find a steep relation (N = 1.4 {+-} 0.2), consistent with a starbursting environment. We measure a [N II]{sub 205{mu}m}/FIR luminosity ratio in APM 08279+5255 and MM 18423+5938 of 9.0 Multiplication-Sign 10{sup -6} and 5.8 Multiplication-Sign 10{sup -6}, respectively. This is in agreement with the decrease of the [N II]{sub 205{mu}m}/FIR ratio at high FIR luminosities observed in local galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

WATER VAPOR EMISSION REVEALS A HIGHLY OBSCURED, STAR-FORMING NUCLEAR REGION IN THE QSO HOST GALAXY APM 08279+5255 AT z = 3.9

We present the detection of four rotational emission lines of water vapor, from energy levels E{sub u}/k = 101-454 K, in the gravitationally lensed z = 3.9 QSO host galaxy APM 08279+5255. While the lowest H{sub 2} O lines are collisionally excited in clumps of warm, dense gas (density of hydrogen nuclei n{sub H} = (3.1 {+-} 1.2) x 10{sup 6} cm{sup -3}, gas temperature T{sub g} {approx} 105 {+-} 21 K), we find that the excitation of the higher lines is dominated by the intense local infrared radiation field. Since only collisionally excited emission contributes to gas cooling, we conclude that H{sub 2} O is not a significant coolant of the warm molecular gas. Our excitation model requires the radiatively excited gas to be located in an extended region of high 100 {mu} m opacity ({tau}{sub 100} = 0.9 {+-} 0.2). Locally, such extended infrared-opaque regions are found only in the nuclei of ultraluminous infrared galaxies. We propose a model where the infrared-opaque circumnuclear cloud, which is penetrated by the X-ray radiation field of the QSO nucleus, contains clumps of massive star formation where the H{sub 2} O emission originates. The radiation pressure from the intense local infrared radiation field exceeds the thermal gas pressure by about an order of magnitude, suggesting close to Eddington-limited star formation in these clumps.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

GAS AND DUST IN A SUBMILLIMETER GALAXY AT z = 4.24 FROM THE HERSCHEL ATLAS

We report ground-based follow-up observations of the exceptional source, ID 141, one of the brightest sources detected so far in the Herschel Astrophysical Terahertz Large Area Survey cosmological survey. ID 141 was observed using the IRAM 30 m telescope and Plateau de Bure interferometer (PdBI), the Submillimeter Array, and the Atacama Pathfinder Experiment submillimeter telescope to measure the dust continuum and emission lines of the main isotope of carbon monoxide and carbon ([C I] and [C II]). The detection of strong CO emission lines with the PdBI confirms that ID 141 is at high redshift (z = 4.243 {+-} 0.001). The strength of the continuum and emission lines suggests that ID 141 is gravitationally lensed. The width ({Delta}V{sub FWHM} {approx} 800 km s{sup -1}) and asymmetric profiles of the CO and carbon lines indicate orbital motion in a disk or a merger. The properties derived for ID 141 are compatible with an ultraluminous (L{sub FIR} {approx} (8.5 {+-} 0.3) x 10{sup 13} {mu}{sup -1}{sub L} L{sub sun}, where {mu}{sub L} is the amplification factor), dense (n {approx} 10{sup 4} cm{sup -3}), and warm (T{sub kin} {approx} 40 K) starburst galaxy, with an estimated star formation rate of (0.7-1.7) x 10{sup 4} {mu}{sup -1}{sub L} M{sub sun} yr{sup -1}. The carbon emission lines indicate a dense (n {approx} 10{sup 4} cm{sup -3}) photon-dominated region, illuminated by a far-UV radiation field a few thousand times more intense than that in our Galaxy. In conclusion, the physical properties of the high-z galaxy ID 141 are remarkably similar to those of local ultraluminous infrared galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

CONSTRUCTING A ONE-SOLAR-MASS EVOLUTIONARY SEQUENCE USING ASTEROSEISMIC DATA FROM KEPLER

Asteroseismology of solar-type stars has entered a new era of large surveys with the success of the NASA Kepler mission, which is providing exquisite data on oscillations of stars across the Hertzsprung-Russell diagram. From the time-series photometry, the two seismic parameters that can be most readily extracted are the large frequency separation ({Delta}{nu}) and the frequency of maximum oscillation power ({nu}{sub max}). After the survey phase, these quantities are available for hundreds of solar-type stars. By scaling from solar values, we use these two asteroseismic observables to identify for the first time an evolutionary sequence of 1 M{sub sun} field stars, without the need for further information from stellar models. Comparison of our determinations with the few available spectroscopic results shows an excellent level of agreement. We discuss the potential of the method for differential analysis throughout the main-sequence evolution and the possibility of detecting twins of very well-known stars.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

EXTENDED SUBMILLIMETER EMISSION OF THE GALACTIC CENTER AND NEAR-INFRARED/SUBMILLIMETER VARIABILITY OF ITS SUPERMASSIVE BLACK HOLE

The innermost tens of parsecs of our Galaxy are characterized by the presence of molecular cloud complexes surrounding Sgr A*, the radiative counterpart of the supermassive black hole ({approx}4 x 10{sup 6} M{sub sun}) at the Galactic center. We seek to distinguish the different physical mechanisms that dominate the molecular clouds at the Galactic center, with special emphasis on the circumnuclear disk (CND). We also want to study the energy flow and model the variable emission of Sgr A*. Our study is based on NIR and submillimeter (sub-mm) observations. Using sub-mm maps, we describe the complex morphology of the molecular clouds and the circumnuclear disk, along with their masses (of order 10{sup 5}-10{sup 6} M{sub sun}), and derive also the temperature and spectral index maps of the regions under study. We conclude that the average temperature of the dust is 14 {+-} 4 K. The spectral index map shows that the 20 and 50 km s{sup -1} clouds are dominated by dust emission. Comparatively, in the CND and its surroundings the spectral indices decrease toward Sgr A* and range between about 1 and -0.6. These values are mostly explained with a combination of dust, synchrotron, and free-free emission in different ratios. The presence of non-thermal emission also accounts for the apparent low temperatures derived in these areas, indicating their unreliability. The Sgr A* light curves show significant flux density excursions in both the NIR and sub-mm domains. We have defined a classification system to account for the NIR variability of Sgr A*. Also, we have modeled on the NIR/sub-mm events. From our modeling results we can infer a sub-mm emission delay with respect to the NIR; we argue that the delay is due to the adiabatic expansion of the synchrotron source components.

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