2,801 research outputs found
Maternal mind-mindedness: a cognitive-behavioural trait or a relational construct?
Background: Maternal mind-mindedness describes mothers’ tendency to attribute internal states to their children (Meins, 1997) and has been shown to have clear links with positive developmental outcomes for children. However, the nature of the construct has not yet been fully explored. Maternal mind-mindedness has been described as both a cognitive-behavioural trait and as a relational construct but crucially designs have included only one child per mother so it has not been possible to investigate whether a mother’s mind-mindedness is related with different children. This thesis aimed to examine the extent to which maternal mind-mindedness can be seen as a cognitive-behavioural trait or a relational construct, dependent on specific mother-child relationships.
Method: Thirty-two mothers with two children between 2½ and 10 years took part in two assessments, nine months apart. Mothers’ relationships with more than one child were investigated concurrently and across time. Mothers’ representational and interactional mind-mindedness were assessed as well as their tendency to use mental-state explanations (psychological mindedness). Child contributions to mind-mindedness were assessed through maternal report and observer ratings of child temperament and behaviour.
Results: Mothers’ representational mind-mindedness was inconsistent across relationships with two children and a partner/friend. Conversely, mothers’ interactional mind-mindedness was found to be highly consistent across relationships with two children. Mothers’ representational and interactional mind-mindedness were not consistently related to their psychological mindedness or to child temperament and behaviour. Representational and interactional measures of mind-mindedness were unrelated.
Conclusion: Support was found for mothers’ representational mind-mindedness as a relational construct and mothers’ interactional mind-mindedness as a trait. However, neither was associated with child temperament and behaviour or reflected a general tendency in the mother to consider psychological factors. The results suggest that representational and interactional maternal mind-mindedness are discrete and should be viewed as different constructs. The theoretical, methodological and practical implications of these findings are discussed
Near Infrared Observations of a Redshift 4.92 Galaxy: Evidence for Significant Dust Absorption
Near-infrared imaging and spectroscopy have been obtained of the
gravitationally lensed galaxy at z=4.92 discovered in HST images by Franx et
al. (1997). Images at 1.2, 1.6 and 2.2 microns show the same arc morphology as
the HST images. The spectrum with resolution \lambda / \Delta\lambda ~ 70 shows
no emission lines with equivalent width stronger than 100 A in the rest frame
wavelength range 0.34 to 0.40 microns. In particular, [OII]3727 A and
[NeIII]3869 A are not seen. The energy distribution is quite blue, as expected
for a young stellar population with the observed Ly alpha flux. The spectral
energy distribution can be fit satisfactorily for such a young stellar
population when absorption by dust is included. The models imply a reddening
0.1 mag < E(B-V) < 0.4 mag. The stellar mass of the lensed galaxy lies in the
range of 2 to 16 x 10^9 Msun. This is significantly higher than estimates based
on the HST data alone. Our data imply that absorption by dust is important to
redshifts of ~5.Comment: LaTeX with ApJ journal format, 2 postscript figures, ApJL, accepte
Spitzer IRAC confirmation of z_850-dropout galaxies in the Hubble Ultra Deep Field: stellar masses and ages at z~7
Using Spitzer IRAC mid-infrared imaging from the Great Observatories Origins
Deep Survey, we study z_850-dropout sources in the Hubble Ultra Deep Field.
After carefully removing contaminating flux from foreground sources, we clearly
detect two z_850-dropouts at 3.6 micron and 4.5 micron, while two others are
marginally detected. The mid-infrared fluxes strongly support their
interpretation as galaxies at z~7, seen when the Universe was only 750 Myr old.
The IRAC observations allow us for the first time to constrain the rest-frame
optical colors, stellar masses, and ages of the highest redshift galaxies.
Fitting stellar population models to the spectral energy distributions, we find
photometric redshifts in the range 6.7-7.4, rest-frame colors U-V=0.2-0.4,
V-band luminosities L_V=0.6-3 x 10^10 L_sun, stellar masses 1-10 x 10^9 M_sun,
stellar ages 50-200 Myr, star formation rates up to ~25 M_sun/yr, and low
reddening A_V<0.4. Overall, the z=7 galaxies appear substantially less massive
and evolved than Lyman break galaxies or Distant Red Galaxies at z=2-3, but
fairly similar to recently identified systems at z=5-6. The stellar mass
density inferred from our z=7 sample is rho* = 1.6^{+1.6}_{-0.8} x 10^6 M_sun
Mpc^-3 (to 0.3 L*(z=3)), in apparent agreement with recent cosmological
hydrodynamic simulations, but we note that incompleteness and sample variance
may introduce larger uncertainties. The ages of the two most massive galaxies
suggest they formed at z>8, during the era of cosmic reionization, but the star
formation rate density derived from their stellar masses and ages is not nearly
sufficient to reionize the universe. The simplest explanation for this
deficiency is that lower-mass galaxies beyond our detection limit reionized the
universe.Comment: 4 pages, 3 figures, emulateapj, Accepted for publication in ApJ
Letter
The Dearth of z~10 Galaxies in all HST Legacy Fields -- The Rapid Evolution of the Galaxy Population in the First 500 Myr
We present an analysis of all prime HST legacy fields spanning >800 arcmin^2
for the search of z~10 galaxy candidates and the study of their UV luminosity
function (LF). In particular, we present new z~10 candidates selected from the
full Hubble Frontier Field (HFF) dataset. Despite the addition of these new
fields, we find a low abundance of z~10 candidates with only 9 reliable sources
identified in all prime HST datasets that include the HUDF09/12, the HUDF/XDF,
all the CANDELS fields, and now the HFF survey. Based on this comprehensive
search, we find that the UV luminosity function decreases by one order of
magnitude from z~8 to z~10 at all luminosities over a four magnitude range.
This also implies a decrease of the cosmic star-formation rate density by an
order of magnitude within 170 Myr from z~8 to z~10. We show that this
accelerated evolution compared to lower redshift can entirely be explained by
the fast build-up of the dark matter halo mass function at z>8. Consequently,
the predicted UV LFs from several models of galaxy formation are in good
agreement with this observed trend, even though the measured UV LF lies at the
low end of model predictions. In particular, the number of only 9 observed
candidate galaxies is lower, by ~50%, than predicted by galaxy evolution
models. The difference is generally still consistent within the Poisson and
cosmic variance uncertainties. However, essentially all models predict larger
numbers than observed. We discuss the implications of these results in light of
the upcoming James Webb Space Telescope mission, which is poised to find much
larger samples of z~10 galaxies as well as their progenitors at less than 400
Myr after the Big Bang.Comment: 13 pages, 6 figures, minor updates to match accepted versio
Low Star Formation Rates for z=1 Early-Type Galaxies in the Very Deep GOODS-MIPS Imaging: Implications for their Optical/Near-Infrared Spectral Energy Distributions
We measure the obscured star formation in z~1 early-type galaxies. This
constrains the influence of star formation on their optical/near-IR colors,
which, we found, are redder than predicted by the model by Bruzual & Charlot
(2003). From deep ACS imaging we construct a sample of 95 morphologically
selected early-type galaxies in the HDF-N and CDF-S with spectroscopic
redshifts in the range 0.85<z<1.15. We measure their 24 micron fluxes from the
deep GOODS-MIPS imaging and derive the IR luminosities and star formation
rates. The fraction of galaxies with >2 sigma detections (~25 muJy} is
17(-4,+9)%. Of the 15 galaxies with significant detections at least six have an
AGN. Stacking the MIPS images of the galaxies without significant detections
and adding the detected galaxies without AGN we find an upper limit on the mean
star formation rate (SFR) of 5.2+/-3.0 Msol yr^-1, and on the mean specific SFR
of 4.6+/-2.2 * 10^-11 yr^-1. Under the assumption that the average SFR will
decline at the same rate as the cosmic average, the in situ growth in stellar
mass of the early-type galaxy population is less than 14+/-7% between z=1 and
the present. We show that the typically low IR luminosity and SFR imply that
the effect of obscured star formation (or AGN) on their rest-frame
optical/near-IR SEDs is negligible for ~90% of the galaxies in our sample.
Hence, their optical/near-IR colors are most likely dominated by evolved
stellar populations. This implies that the colors predicted by the Bruzual &
Charlot (2003) model for stellar populations with ages similar to those of z~1
early-type galaxies (~1-3 Gyr) are most likely too blue, and that stellar
masses of evolved, high-redshift galaxies can be overestimated by up to a
factor of ~2.Comment: Accepted for publication in ApJ, 8 pages, 4 figures, 1 tabl
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