Kirsten Kraiberg Knudsen

Publications (4)10.92 Total impact

• Source

  Available from: arxiv.org

  Article: Stellar populations and kinematics of red galaxies at z > 2: Implications for the formation of massive galaxies

  Pieter G. van Dokkum, Marijn Franx, Natascha M. Förster Schreiber, Garth D. Illingworth, Emanuele Daddi, Kirsten Kraiberg Knudsen, Ivo Labbé, Alan Moorwood, Hans-Walter Rix, Huub Röttgering, Gregory Rudnick, Ignacio Trujillo, Paul van der Werf, Arjen van der Wel, Lottie van Starkenburg, Stijn Wuyts
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  ABSTRACT: We recently identified a substantial population of galaxies at z‚‚gt;2 with comparatively red rest-frame optical colors. These distant red galaxies (DRGs) are efficiently selected by the simple observed color criterion Js-Ks‚‚gt;2.3. In this paper we present near-infrared spectroscopy with Keck NIRSPEC of six DRGs with previously measured redshifts 2.4‚‚lt;z‚‚lt;3.2, two of which were known to host an active nucleus. We detect continuum emission and emission lines of all observed galaxies. Equivalent widths of H‚‚alpha; in the nonactive galaxies are 20-30 ‚‚Aring;, smaller than measured for Lyman break galaxies (LBGs) and nearby luminous infrared galaxies and comparable to normal nearby galaxies. The modest equivalent widths imply that the galaxies either have a decreasing star formation rate or are very dusty. Fitting both the photometry and the H‚‚alpha; lines, we find continuum extinction AV=1-2 mag, ages 1-2.5 Gyr, star formation rates 200-400 Msolar yr-1, and stellar masses (1-5)‚‚times;1011 Msolar for models with constant star formation rates. Models with a declining star formation lead to significantly lower extinction, star formation rates, and ages but similar stellar masses. From [N II]/H‚‚alpha; ratios we infer that the metallicities are high, 1-1.5 times solar. For four galaxies we can determine line widths from the optical emission lines. The widths are high, ranging from 130 to 240 km s-1, and by combining data for LBGs and DRGs, we find significant correlations between line width and rest-frame U-V color and between line width and stellar mass. The latter correlation has a similar slope and offset as the ``baryonic Tully-Fisher relation'' for nearby galaxies. From the line widths and effective radii we infer dynamical masses and mass-to-light (M/L) ratios. The median dynamical mass is ~2‚‚times;1011 Msolar, supporting the high stellar masses inferred from the photometry. We find that the median M/LV~0.8(M/L)solar, a factor of ~5 higher than measured for LBGs. We infer from our small sample that DRGs are dustier, more metal-rich, and more massive and have higher ages than z~3 LBGs of the same rest-frame V-band luminosity. Although their volume density is still uncertain, their high M/L ratios imply that they contribute significantly to the stellar mass density at z~2.5. As their stellar masses are comparable to those of early-type galaxies, they may have already assembled most of their final mass.
  The Astrophysical Journal 12/2008; · 6.02 Impact Factor
• Source

  Available from: arxiv.org

  Article: Multiply-imaged submm galaxy in a z~2.5 group

  Jean-Paul Kneib, Paul P. van der Werf, Kirsten Kraiberg Knudsen, Ian Smail, Andrew Blain, Dave Frayer, Vicki Barnard, Rob Ivison
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  ABSTRACT: We present observations of a remarkable submillimetre-selected galaxy, SMMJ16359+6612. This distant galaxy lies behind the core of a massive cluster of galaxies, A2218, and is gravitationally lensed by the foreground cluster into three discrete images which were identified in deep submillimetre maps of the cluster core at both 450 and 850micron. Subsequent follow-up using deep optical and NIR images identify a faint counterpart to each of the 3 images, with similar red optical--NIR colours and HST morphologies. By exploiting a detailed mass model for the cluster lens we estimate that the combined images of this galaxy are magnified by a factor of ~45, implying that this galaxy would have un-lensed magnitudes K_s=22.9 and I=26.1, and an un-lensed 850micron flux density of only 0.8mJy. Moreover, the highly constrained lens model predicted the redshift of SMMJ16359+6612 to be z=2.6+/-0.4. We confirm this estimate using deep optical and NIR Keck spectroscopy, measuring a redshift of z=2.516. SMMJ16359+6612 is the faintest submm-selected galaxy so far identified with a precise redshift. Thanks to the large gravitational magnification of this source, we identify 3 sub-components in this submm galaxy, which are also seen in the NIRSPEC data, arguing for either a strong dust (lane) absorption or a merger. Interestingly, there are 2 other highly-amplified galaxies at almost identical redshifts in this field (although neither is a strong submm emitter). The 3 galaxies lie within a ~100kpc region on the background sky, suggesting this submm galaxy is located in a dense high-redshift group. Comment: 7 pages, 1 JPEG figure, MNRAS in press
  03/2004;
• Article: A multiply imaged, submillimetre‐selected ultraluminous infrared galaxy in a galaxy group at z∼ 2.5

  Jean-Paul Kneib, Paul P. Van Der Werf, Kirsten Kraiberg Knudsen, Ian Smail, Andrew Blain, Dave Frayer, Vicki Barnard, Rob Ivison
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  ABSTRACT: We present observations of a remarkable submillimetre-selected galaxy, SMM J16359+6612. This distant galaxy lies behind the core of a massive cluster of galaxies, A 2218, and is gravitationally lensed by the foreground cluster into three discrete images which were identified in deep submillimetre maps of the cluster core at both 450 and 850 μm. Subsequent follow-up investigations using deep optical and near-infrared (NIR) images identify a faint counterpart to each of the three images, with similar red optical–NIR colours and Hubble Space Telescope morphologies. By exploiting a detailed mass model for the cluster lens we estimate that the combined images of this galaxy are magnified by a factor of ∼45, implying that this galaxy would have unlensed magnitudes Ks= 22.9 and I= 26.1, and an unlensed 850-μm flux density of only 0.8 mJy. Moreover, the highly constrained lens model predicted the redshift of SMM J16359+6612 to be z= 2.6 ± 0.4. We confirm this estimate using deep optical and NIR Keck spectroscopy, measuring a redshift of z= 2.516. SMM J16359+6612 is the faintest submillimetre (submm)-selected galaxy so far identified with a precise redshift. Thanks to the large gravitational magnification of this source, we identify three sub-components in this submm galaxy, which are also seen in the Near Infrared Spectrograph (NIRSPEC) data, arguing for either a strong dust (lane) absorption or a merger. Interestingly, there are two other highly amplified galaxies at almost identical redshifts in this field (although neither is a strong submm emitter). The three galaxies lie within a ∼100-kpc region on the background sky, suggesting this submm galaxy is located in a dense high-redshift group.
  Monthly Notices of the Royal Astronomical Society 02/2004; 349(4):1211 - 1217. · 4.90 Impact Factor
• Source

  Available from: ArXiv

  Article: Can dusty Lyman break galaxies produce the submillimeter counts and background? Lessons from lensed Lyman break galaxies

  Paul P. van der Werf, Kirsten Kraiberg Knudsen, Ivo Labbe, Marijn Franx
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  ABSTRACT: Can the submillimeter counts and background be produced by applying a locally derived extinction correction to the population of Lyman break galaxies? We investigate the submillimeter emission of two strongly lensed Lyman break galaxies (MS1512+36-cB58 and MS1358+62-G1) and find that the procedure that is used to predict the submillimeter emission of the Lyman break galaxy population overpredicts the observed 850micron fluxes by up to a factor of 14. This result calls for caution in applying local correlations to distant galaxies. It also shows that large extinction corrections on Lyman break galaxies should be viewed with skepticism. It is concluded that the Lyman break galaxies may contribute to the submillimeter background at the 25 to 50% level. The brighter submillimeter galaxies making up the rest of the background are either not detected in optical surveys, or if they are detected, their submillimeter emission cannot be reliably estimated from their rest-frame ultraviolet properties.
  11/2000;