148 research outputs found
Jet-ISM Interaction in the Radio Galaxy 3C293: Jet-driven Shocks Heat ISM to Power X-ray and Molecular H2 emission
We present a 70ks Chandra observation of the radio galaxy 3C293. This galaxy
belongs to the class of molecular hydrogen emission galaxies (MOHEGs) that have
very luminous emission from warm molecular hydrogen. In radio galaxies, the
molecular gas appears to be heated by jet-driven shocks, but exactly how this
mechanism works is still poorly understood. With Chandra, we observe X-ray
emission from the jets within the host galaxy and along the 100 kpc radio jets.
We model the X-ray spectra of the nucleus, the inner jets, and the X-ray
features along the extended radio jets. Both the nucleus and the inner jets
show evidence of 10^7 K shock-heated gas. The kinetic power of the jets is more
than sufficient to heat the X-ray emitting gas within the host galaxy. The
thermal X-ray and warm H2 luminosities of 3C293 are similar, indicating similar
masses of X-ray hot gas and warm molecular gas. This is consistent with a
picture where both derive from a multiphase, shocked interstellar medium (ISM).
We find that radio-loud MOHEGs that are not brightest cluster galaxies (BCGs),
like 3C293, typically have LH2/LX~1 and MH2/MX~1, whereas MOHEGs that are BCGs
have LH2/LX~0.01 and MH2/MX~0.01. The more massive, virialized, hot atmosphere
in BCGs overwhelms any direct X-ray emission from current jet-ISM interaction.
On the other hand, LH2/LX~1 in the Spiderweb BCG at z=2, which resides in an
unvirialized protocluster and hosts a powerful radio source. Over time, jet-ISM
interaction may contribute to the establishment of a hot atmosphere in BCGs and
other massive elliptical galaxies.Comment: Accepted by ApJ 21 pages in ApJ format, 9 figures, 8 table
Optimal Point-Source Extraction for Spitzer IRS Spectra
A new optimal-extraction technique has been developed for deriving point-source spectra from data taken by the Infrared Spectrograph (IRS) on-board the Spitzer Space Telescope. The new technique gives improvements of up to a factor of two in the signal-to-noise ratio (S/N) for faint (< 10 mJy) sources, corresponding to an effective quadrupling of the exposure time. Regular extraction consists of an even-weighted summing of pixel values at the same wavelength. Optimal extraction weights each pixel by its S/N, estimated using the spatial profile of a bright calibration star and data uncertainties. Additionally,
the optimal-extraction calculations are performed in “rectified” space, and so a natural by-product of the processing is a useful output file containing the
rectified image. The optimal-extraction technique is unsuitable for extended sources and best only for point sources
Polarization and Structure of Broad Absorption Line Quasi-Stellar Objects
This thesis is a spectropolarimetric survey of broad absorption line quasi-stellar objects (BAL QSO). We observed 36 BAL QSO at low resolution with the 5 m Hale Telescope at Palomar Observatory and the 10 m Keck Telescopes at the W. M. Keck Observatory.
The continuum, absorption trough, and emission line polarization of BAL QSO were studied in detail, yielding clues about the geometrical structure of gas in the inner regions of quasars. BAL QSO have, on average, higher polarization than other quasars, reinforcing the view that they are normal quasars viewed from a more equatorial aspect. However, there is a wide distribution of polarization values, which may be due to intrinsic differences in the geometry or optical depth to scattering. No correlations are found among emission line or broad absorption line properties and continuum polarization, suggesting that these properties are regulated by internal differences unrelated to viewing angle. The continuum polarization of BAL QSO is weakly wavelength dependent after correction for emission line dilution. In most objects, the polarization rises to the blue, suggesting that dust scattering or absorption may be important.
Broad emission line photons are polarized less than the continuum; and the position angle of the electric vector is rotated with respect to the continuum. The semi-forbidden C III] emission line is polarized differently than the C IV emission line in some cases, suggesting resonance scattering in the C III] emission line region. Resonantly scattered photons from the broad absorption line region are detected at high velocities red-ward and blue-ward of the C IV line center in the spectra of some objects. These photons are negatively polarized with respect to the continuum photons, showing that the broad absorption line region and the continuum scattering region are oriented perpendicular to each other.
The polarization increases in the BAL troughs, due mainly to partial coverage of the central source by the broad absorption line region. Partial coverage of the continuum and broad emission line clouds leads to difficulties in determining the true optical depth of the BAL outflow. The geometry of the intervening BAL clouds is skewed with respect to the continuum scattering region, which results in position angle rotations in the BAL. The variation of polarization with velocity in the BAL is consistent with a non-radial, accelerating outflow of ionized gas. Our polarimetry observations are consistent with a model which unifies BAL QSO and non-BAL QSO. The BAL wind appears to occupy a narrow range of equatorial latitudes. When we view a QSO through this outflow, we see the characteristic troughs in BAL QSO.</p
Superluminous Spiral Galaxies
We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster galaxies, with r-band monochromatic luminosity L_r = 8–14L* (4.3–7.5 × 10^(44) erg s^(−1)). These super spiral galaxies are also giant and massive, with diameter D = 57–134 kpc and stellar mass M_(stars) = 0.3–3.4 × 10^(11)M⊙. We find 53 super spirals out of a complete sample of 1616 SDSS galaxies with redshift z 8L*. The closest example is found at z = 0.089. We use existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS and Wide-field Infrared Survey Explorer colors are consistent with normal star-forming spirals on the blue sequence. However, the extreme masses and rapid SFRs of 5–65 M⊙ yr^(−1) place super spirals in a sparsely populated region of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a diverse range of environments, from isolation to cluster centers. We find four super spiral galaxy systems that are late-stage major mergers—a possible clue to their formation. We suggest that super spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become massive lenticular galaxies after they are cut off from their gas supply and their disks fade
Star Formation Suppression Due to Jet Feedback in Radio Galaxies with Shocked Warm Molecular Gas
We present Herschel observations of 22 radio galaxies, selected for the presence of shocked, warm molecular hydrogen emission. We measured and modeled spectral energy distributions in 33 bands from the ultraviolet to the far-infrared to investigate the impact of jet feedback on star formation activity. These galaxies are massive, early-type galaxies with normal gas-to-dust ratios, covering a range of optical and infrared colors. We find that the star formation rate (SFR) is suppressed by a factor of ~3–6, depending on how molecular gas mass is estimated. We suggest that this suppression is due to the shocks driven by the radio jets injecting turbulence into the interstellar medium (ISM), which also powers the luminous warm H_2 line emission. Approximately 25% of the sample shows suppression by more than a factor of 10. However, the degree of SFR suppression does not correlate with indicators of jet feedback including jet power, diffuse X-ray emission, or intensity of warm molecular H_2 emission, suggesting that while injected turbulence likely impacts star formation, the process is not purely parameterized by the amount of mechanical energy dissipated into the ISM. Radio galaxies with shocked warm molecular gas cover a wide range in SFR–stellar mass space, indicating that these galaxies are in a variety of evolutionary states, from actively star-forming and gas-rich to quiescent and gas-poor. SFR suppression appears to have the largest impact on the evolution of galaxies that are moderately gas-rich
Jet-related Excitation of the [CII] Emission in the Active Galaxy NGC 4258 with SOFIA
We detect widespread [CII]157.7um emission from the inner 5 kpc of the active
galaxy NGC 4258 with the SOFIA integral field spectrometer FIFI-LS. The
emission is found associated with warm H2, distributed along and beyond the end
of southern jet, in a zone known to contain shock-excited optical filaments. It
is also associated with soft X-ray hot-spots, which are the counterparts of the
`anomalous radio arms' of NGC~4258, and a 1 kpc-long filament on the minor axis
of the galaxy which contains young star clusters. Palomar-CWI H-alpha integral
field spectroscopy shows that the filament exhibits non-circular motions within
NGC 4258. Many of the [CII] profiles are very broad, with the highest line
width, 455 km/s, observed at the position of the southern jet bow-shock.
Abnormally high ratios of L([CII])/L(FIR) and L([CII])/L(PAH7.7um) are found
along and beyond the southern jet and in the X-ray hotspots. These are the same
regions that exhibit unusually large intrinsic [CII] line widths. This suggests
that the [CII] traces warm molecular gas in shocks and turbulence associated
with the jet. We estimate that as much as 40% (3.8 x 10^39 erg/s) of the total
[CII] luminosity from the inner 5 kpc of NGC 4258 arises in shocks and
turbulence (< 1% bolometric luminosity from the active nucleus), the rest being
consistent with [CII] excitation associated with star formation. We propose
that the highly-inclined jet is colliding with, and being deflected around,
dense irregularities in a thick disk, leading to significant energy dissipation
over a wide area of the galaxy.Comment: Accepted for Publication in the Astrophysical Journal Oct 29 201
Cygnus A Obscuring Torus: Ionized, Atomic or Molecular?
The prototypical powerful FR \Romannum{2} radio galaxy Cygnus A fits
extremely well into the quasar/radio galaxy unified model: high polarization
with an angle almost perpendicular to the radio jet and polarized flux showing
broad permitted lines. It has been claimed that ionized gas in the torus
reveals a very clear torus shape via Bremmstrahlung emission. We rule out the
later with an energetic argument, and we constrain the molecular and atomic gas
properties with existing observations. The atomic absorption against the core
has been shown to match the X-ray column only if the spin temperature is an
implausible K. This points to a molecular medium for
the X-ray column . Yet not low-J CO
absorption is detected to sensitive limits. The non-detection is surprising
given that this powerful radio galaxy hosts a luminous, dust-obscured active
nucleus and copious warm molecular hydrogen. These conditions suggest a
detectable level of emission. Furthermore, the torus X-ray column density
suggests detectable absorption. We explore various possibilities to explain the
lack of a signature from warm CO (200-250K). Specifically, that the radiative
excitation by the radio core renders low-J CO absorption below current
sensitivities, and that high-J levels are well populated and conducive to
producing absorption. We test this hypothesis using archival
\textit{Hershel}/SPIRE FTS observations of Cygnus A of high-J CO lines ( transitions). Still high-J CO lines are not detected. We suggest
that ALMA observations near its high frequency limit can be critical to obtain
the signature of molecular line of the torus of Cygnus A
A Catalog of the Most Optically Luminous Galaxies at z < 0.3: Super Spirals, Super Lenticulars, Super Post-Mergers, and Giant Ellipticals
We present a catalog of the 1525 most optically luminous galaxies from the Sloan Digital Sky Survey with r-band luminosity L_r > 8L* and redshift z < 0.3, including 84 super spirals, 15 super lenticulars, 14 super post-merger galaxies, and 1400 giant ellipticals. With mass in stars of 10^(11.3)–10^(12) M⊙, super spirals and lenticulars are the most massive disk galaxies currently known. The specific star formation rates of super spirals place them on or below the star-forming main sequence. They must have formed stars at a high rate throughout their history in order to grow their massive, gigantic stellar disks and maintain their blue u − r integrated colors. Their disks are red on the inside and blue on the outside, consistent with inside-out growth. They tend to have small bulge-to-total (B/T) r-band luminosity ratios, characteristic of disk building via minor mergers and cold accretion. A large percentage of super disk galaxies (41%) have double nuclei, double disks, or other signatures of ongoing mergers. Most (72%) are found in moderate- to low-density environments, while the rest are found at the outskirts of clusters. It is likely that super spirals survive in these environments because they continue to accrete cold gas and experience only minor mergers at late times, by virtue of their enormous masses and angular momenta. We suggest that super post-mergers are the product of super spiral major mergers and may be the precursors of some giant elliptical galaxies found in low-density environments. We present two new gravitational lens candidates in an appendix
- …