arXiv subjects

E. T. Young

Publications and source records attributed to E. T. Young.

34 records · Page 2Linked to original sources

arXiv2006

Spitzer/MIPS Infrared Imaging of M31: Further Evidence for a Spiral/Ring Composite Structure

New images of M31 at 24, 70, and 160 micron taken with the Multiband Imaging Photometer for Spitzer (MIPS) reveal the morphology of the dust in this galaxy. This morphology is well represented by a composite of two logarithmic spiral arms and a circular ring (radius ~10 kpc) of star formation offset from the nucleus. The two spiral arms appear to start at the ends of a bar in the nuclear region and extend beyond the star forming ring. As has been found in previous work, the spiral arms are not continuous but composed of spiral segments. The star forming ring is very circular except for a region near M32 where it splits. The lack of well defined spiral arms and the prominence of the nearly circular ring suggests that M31 has been distorted by interactions with its satellite galaxies. Using new dynamical simulations of M31 interacting with M32 and NGC 205 we find that, qualitatively, such interactions can produce an offset, split ring like that seen in the MIPS images.

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arXiv2006

Spitzer and Magellan Observations of NGC 2264: A Remarkable Star Forming Core Near IRS-2

We analyze {\it Spitzer} and Magellan observations of a star forming core near IRS-2 in the young cluster NGC 2264. The submillimeter source IRAS 12 S1, previously believed to be an intermediate mass Class 0 object is shown to be a dense collection of embedded, low mass stars. We argue that this group of stars represents the fragmenting collapse of a dense, turbulent core, based on a number of indicators of extreme youth. With reasonable estimates for the velocity dispersion in the group, we estimate a dynamical lifetime of only a few x 10$^{4}$ years. Spectral energy distributions of stars in the core are consistent with Class I or Class 0 assignments. We present observations of an extensive system of molecular hydrogen emission knots. The luminosity of the objects in the core region are consistent with roughly solar mass protostars.

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arXiv2005

Bispectrum speckle interferometry of the massive protostellar outflow source IRAS 23151+5912

We present bispectrum speckle interferometry of the massive protostellar object IRAS 23151+5912 in the near-infrared K' band. The reconstructed image shows the diffuse nebulosity north-east of two point-like sources in unprecedented detail. The comparison of our near-infrared image with mm continuum and CO molecular line maps shows that the brighter of the two point sources lies near the center of the mm peak, indicating that it is a high-mass protostar. The nebulosity coincides with the blue-shifted molecular outflow component. The most prominent feature in the nebulosity is a bow-shock-like arc. We assume that this feature is associated with a precessing jet which has created an inward-pointed cone in the swept-up material. We present numerical jet simulations that reproduce this and several other features observed in our speckle image of the nebulosity. Our data also reveal a linear structure connecting the central point source to the extended diffuse nebulosity. This feature may represent the innermost part of a jet that drives the strong molecular outflow (PA ~80 degr) from IRAS 23151+5912. With the aid of radiative transfer calculations, we demonstrate that, in general, the observed inner structures of the circumstellar material surrounding high-mass stars are strongly influenced by the orientation and symmetry of the bipolar cavity.

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arXiv2005

A New Large-Well 1024x1024 Si:As Detector for the Mid-Infrare

We present a description of a new 1024x1024 Si:As array designed for ground-based use from 5 - 28 microns. With a maximum well depth of 5e6 electrons, this device brings large-format array technology to bear on ground-based mid-infrared programs, allowing entry to the megapixel realm previously only accessible to the near-IR. The multiplexer design features switchable gain, a 256x256 windowing mode for extremely bright sources, and it is two-edge buttable. The device is currently in its final design phase at DRS in Cypress, CA. We anticipate completion of the foundry run in the beginning of 2006. This new array will enable wide field, high angular resolution ground-based follow up of targets found by space-based missions such as the Spitzer Space Telescope and the Widefield Infrared Survey Explorer (WISE).

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arXiv2005

Infrared Echoes near the Supernova Remnant Cassiopeia A

Two images of Cassiopeia A obtained at 24 micrometer with the Spitzer Space Telescope over a one year time interval show moving structures outside the shell of the supernova remnant to a distance of more than 20 arcmin. Individual features exhibit apparent motions of 10 to 20 arcsec per year, independently confirmed by near-infrared observations. The observed tangential velocities are at roughly the speed of light. It is likely that the moving structures are infrared echoes, in which interstellar dust is heated by the explosion and by flares from the compact object near the center of the remnant.

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arXiv2005

Reduction Algorithms for the Multiband Imaging Photometer for Spitzer: 6 Months of Flight Data

The first six months of flight data from the Multiband Imaging Photometer for Spitzer (MIPS) were used to test MIPS reduction algorithms based on extensive preflight laboratory data and modeling. The underlying approach for the preflight algorithms has been found to be sound, but some modifications have improved the performance. The main changes are scan mirror dependent flat fields at 24 micron, hand processing to remove the time dependent stim flash latents and fast/slow response variations at 70 micron, and the use of asteroids and other sources instead of stars for flux calibration at 160 micron due to a blue ``leak.'' The photometric accuracy of flux measurpements is currently 5%, 10%, and 20% at 24, 70, and 160 micron, respectively. These numbers are expected to improve as more flight data are analyzed and data reduction algorithms refined.

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arXiv2005

Reduction Algorithms for the Multiband Imaging Photometer for Spitzer

We describe the data reduction algorithms for the Multiband Imaging Photometer for Spitzer (MIPS) instrument. These algorithms were based on extensive preflight testing and modeling of the Si:As (24 micron) and Ge:Ga (70 and 160 micron) arrays in MIPS and have been refined based on initial flight data. The behaviors we describe are typical of state-of-the-art infrared focal planes operated in the low backgrounds of space. The Ge arrays are bulk photoconductors and therefore show a variety of artifacts that must be removed to calibrate the data. The Si array, while better behaved than the Ge arrays, does show a handful of artifacts that also must be removed to calibrate the data. The data reduction to remove these effects is divided into three parts. The first part converts the non-destructively read data ramps into slopes while removing artifacts with time constants of the order of the exposure time. The second part calibrates the slope measurements while removing artifacts with time constants longer than the exposure time. The third part uses the redundancy inherit in the MIPS observing modes to improve the artifact removal iteratively. For each of these steps, we illustrate the relevant laboratory experiments or theoretical arguments along with the mathematical approaches taken to calibrate the data. Finally, we describe how these preflight algorithms have performed on actual flight data.

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arXiv2004

The Outburst of V1647 Ori Revealed by Spitzer

We present Spitzer Space Telescope observations of V1647 Ori, the outbursting source lighting McNeil's nebula, taken near the optical peak of the outburst in early March 2004. The source is easily detected in all Spitzer imaging bands from 3.6 - 70 microns. The fluxes at all wavelengths are roughly a factor of 15 brighter than pre-outburst levels; we measure a bolometric luminosity of 44 Lsun. We posit that this event is due to an increase in the accretion luminosity of the source. Simple models of an accretion disk plus tenuous envelope can qualitatively explain the observed pre- and post-outburst spectral energy distributions. The accretion activity implied by our results indicates that the outburst may be intermediate between FUor and EXor-type events. We also report the discovery of a previously unknown mid-infrared counterpart to the nearby Herbig-Haro object HH 22.

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arXiv2004

Far Infrared Source Counts at 70 and 160 microns in Spitzer Deep Surveys

We derive galaxy source counts at 70 and 160 microns using the Multiband Imaging Photometer for Spitzer (MIPS) to map the Chandra Deep Field South (CDFS) and other fields. At 70 microns, our observations extend upwards about 2 orders of magnitude in flux density from a threshold of 15 mJy, and at 160 microns they extend about an order of magnitude upward from 50 mJy. The counts are consistent with previous observations on the bright end. Significant evolution is detected at the faint end of the counts in both bands, by factors of 2-3 over no-evolution models. This evolution agrees well with models that indicate most ofthe faint galaxies lie at redshifts between 0.7 and 0.9. The new Spitzer data already resolve about 23% of the Cosmic Far Infrared Background at 70 microns and about 7% at 160 microns.

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arXiv2004

Identification of luminous infrared galaxies at 1<z<2.5

We present preliminary results on 24micron detections of luminous infrared galaxies at z>1 with the Multiband Imaging Photometer for Spitzer (MIPS). Observations were performed in the Lockman Hole and the Extended Groth Strip (EGS), and were supplemented by data obtained with the Infrared Array Camera (IRAC) between 3 and 9microns. The positional accuracy of ~2arcsec for most MIPS/IRAC detections provides unambiguous identifications of their optical counterparts. Using spectroscopic redshifts from the Deep Extragalactic Evolutionary Probe survey, we identify 24micron sources at z>1 in the EGS, while the combination of the MIPS/IRAC observations with $BVRIJHK$ ancillary data in the Lockman Hole also shows very clear cases of galaxies with photometric redshifts at 1 =M*) galaxy counterparts. It is the first time that this population of luminous objects is detected up to z~2.5 in the infrared. Our work demonstrates the ability of the MIPS instrument to probe the dusty Universe at very high redshift, and illustrates how the forthcoming Spitzer deep surveys will offer a unique opportunity to illuminate a dark side of cosmic history not explored by previous infrared experiments.

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arXiv2004

Far Infrared Imaging of NGC 55

We present images of the galaxy NGC 55 at 24, 70, and 160 micron obtained with the Multiband Imaging Photometer for Spitzer (MIPS) instrument aboard the Spitzer Space Telescope. The new images display the far infrared emission in unprecedented detail and demonstrate that the infrared morphology differs dramatically from that at shorter wavelengths. The most luminous emission region in the galaxy is marginally resolved at 24 micron and has a projected separation of nearly 520 pc from the peak emission in the optical and near infrared. This region is responsible for ~9% of the total emission at 24 micron and is likely a young star formation region. We show that this and other compact sources account for more than 1/3 of the total 24 micron emission. We compute a total infrared luminosity for NGC 55 of 1.2*10^9 L_sun. The star formation rate implied by our measurements is 0.22 M_sun/yr. We demonstrate that the cold dust is more extended than the warm dust in NGC 55--the minor-axis scale heights are 0.32, 0.43, and 0.49 kpc at 24, 70 and 160 micron, respectively. The dust temperature map shows a range of temperatures that are well-correlated with the 24 micron surface brightness, from 20 K in low-surface-brightness regions to 26 K in high-surface-brightness regions.

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arXiv2004

The 24-Micron View of Embedded Star Formation in NGC 7129

We present observations of the star formation region NGC 7129 taken with the Multiband Imaging Photometer for Spitzer (MIPS). A significant population of sources, likely pre-main sequence members of the young stellar cluster, is revealed outside the central photoionization region. Combining with Infrared Array Camera (IRAC) and ground-based near-infrared images, we have obtained colors and spectral energy distributions for some 60 objects. The [3.6]-[4.5] vs. [8]-[24] color-color plane shows sources clustered at several different loci, which roughly correspond to the archetypal evolutionary sequence Class 0, I, II, and III. We obtain preliminary classifications for 36 objects, and find significant numbers of both Class I and II objects. Most of the pre-main sequence candidates are associated with the densest part of the molecular cloud surrounding the photoionization region, indicating active star formation over a broad area outside the central cluster. We discuss three Class II candidates that exhibit evidence of inner disk clearing, which would be some of the youngest known examples of a transition from accretion to optically thin quiescent disks.

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arXiv2004

Spatially Resolved Ultraviolet, H-alpha, Infrared, and Radio Star Formation in M81

We present Multiband Imaging Photometer for Spitzer (MIPS) observations of M81 at 24, 70, and 160 micron. The grand design nature of M81 is clearly seen, showing two well resolved spiral arms containing numerous bright star forming regions. The MIPS images reveal a significant amount of cold dust associated with the spiral arms. We investigate the variation of the ultraviolet (UV), H-alpha, and infrared (IR) luminosities and star formation rate (SFR) indicators across the face of M81 using the MIPS images and archival UV and H-alpha images. For regions in M81, we find that UV and H-alpha SFRs (uncorrected for dust attenuation) are always lower than the IR SFR. The cause of this behavior is dust attenuation and/or using SFR calibrations appropriate for entire galaxies, not regions in galaxies. The characteristics of the dust attenuation for the regions indicate the dust grains and/or geometry are different from those in starburst galaxies. The behavior of the infrared-radio correlation in M81 is seen to vary from the global average, with variations correlated with the morphology of M81.

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arXiv2004

Confusion in the infrared: Spitzer and beyond

We use the source counts measured with the Multiband Imaging Photometer for Spitzer (MIPS) at 24, 70, and 160 microns to determine the 5-sigma confusion limits due to extragalactic sources: 56 micro-Jy, 3.2 and 40 mJy at 24, 70 and 160 microns, respectively. We also make predictions for confusion limits for a number of proposed far infrared missions of larger aperture (3.5 to 10m diameter).

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arXiv2004

The 24 Micron Source Counts in Deep Spitzer Surveys

Galaxy source counts in the infrared provide strong constraints on the evolution of the bolometric energy output from distant galaxy populations. We present the results from deep 24 micron imaging from Spitzer surveys, which include approximately 50,000 sources to an 80% completeness of 60 uJy. The 24 micron counts rapidly rise at near-Euclidean rates down to 5 mJy, increase with a super-Euclidean rate between 0.4 - 4 mJy, and converge below 0.3 mJy. The 24 micron counts exceed expectations from non-evolving models by a factor >10 at 0.1 mJy. The peak in the differential number counts corresponds to a population of faint sources that is not expected from predictions based on 15 micron counts from ISO. We argue that this implies the existence of a previously undetected population of infrared-luminous galaxies at z ~ 1-3. Integrating the counts to 60 uJy, we derive a lower limit on the 24 micron background intensity of 1.9 +/- 0.6 nW m-2 sr-1 of which the majority (~ 60%) stems from sources fainter than 0.4 mJy. Extrapolating to fainter flux densities, sources below 60 uJy contribute 0.8 {+0.9/-0.4} nW m-2 sr-1 to the background, which provides an estimate of the total 24 micron background of 2.7 {+1.1/-0.7} nW m-2 sr-1.

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arXiv2003

Using Narrow Band Photometry to Classify Stars and Brown Dwarfs

We present a new system of narrow band filters in the near infrared that can be used to classify stars and brown dwarfs. This set of four filters, spanning the H band, can be used to identify molecular features unique to brown dwarfs, such as H2O and CH4. The four filters are centered at 1.495 um (H2O), 1.595 um (continuum), 1.66 um (CH4), and 1.75 um (H2O). Using two H2O filters allows us to solve for individual objects' reddenings. This can be accomplished by constructing a color-color-color cube and rotating it until the reddening vector disappears. We created a model of predicted color-color-color values for different spectral types by integrating filter bandpass data with spectra of known stars and brown dwarfs. We validated this model by making photometric measurements of seven known L and T dwarfs, ranging from L1 - T7.5. The photometric measurements agree with the model to within +/-0.1 mag, allowing us to create spectral indices for different spectral types. We can classify A through early M stars to within +/-2 spectral types, late-type M and L dwarfs to within +/-0.3 spectral types and T dwarfs to within +/-0.1 spectral types 1-sigma. Thus, we can distinguish between a T1 and a T3 dwarf. The four physical bands can be converted into two reddening-free indices, mu1 and mu2, and an extinction, AV, for the individual object. This technique, which is equivalent to extremely low resolution spectroscopy, can be used to survey large areas to provide rough spectral classifications for all the stars in the area, ranging down to the coolest brown dwarfs. It should prove particularly useful in young clusters where reddening can be high.

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