Metallicity Effects on Mid-Infrared Colors and the 8 micron PAH Emission in Galaxies

a r X i v :a s t r o -p h /0506214v 1 9 J u n 2005

Draft version February 2,2008

Preprint typeset using L A T E X style emulateapj v.6/22/04

METALLICITY EFFECTS ON MID-INFRARED COLORS AND THE 8μm PAH EMISSION IN GALAXIES

C.W.Engelbracht 1,K.

D.Gordon 1,G.H.Rieke 1,M.W.Werner 2,D.A.Dale 3,and https://www.sodocs.net/doc/6e12516925.html,tter 4

Draft version February 2,2008

ABSTRACT

We examine colors from 3.6μm to 24μm as a function of metallicity (O/H)for a sample of 34galaxies.The galaxies range over 2orders of magnitude in metallicity.They display an abrupt shift in the 8μm to 24μm color between metallicities 1/3to 1/5of the solar value.The mean 8μm to 24μm ?ux density ratio below and above 12+log (O/H )=8.2is 0.08±0.04and 0.70±0.53,respectively.We use mid-infrared colors and spectroscopy to demonstrate that the shift is primarily due to a decrease in the 8μm ?ux density as opposed to an increase in the 24μm ?ux density.This result is most simply interpreted as due to a weakening at low metallicity of the mid-infrared emission bands usually attributed to PAHs (polycyclic aromatic hydrocarbons)relative to the small-grain dust emission.However,existing empirical spectral energy distribution models cannot account for the observed short-wavelength (i.e.,below 8μm)colors of the low-metallicity galaxies merely by reducing the strength of the PAH features;some other emission source (e.g.,hot dust)is required.Subject headings:galaxies:ISM—infrared:galaxies

1.INTRODUCTION

Early galaxies must have formed at a very low metal-licity.Such galaxies likely had di?erent properties from typical galaxies observed in the local universe,where gen-erations of star formation have enriched the ISM (in-terstellar medium).These early galaxies are di?cult to study because they are so distant.As a result,nearby low-metallicity galaxies have generated considerable in-terest as local analogs of young galaxies at high redshift

(see,for example,the review by Kunth &¨Ostlin 2000).

Understanding the infrared properties of nearby low metallicity galaxies will help guide interpreta-tion of Spitzer observations of high-redshift ones (e.g.,Fazio et al.2004;Yan et al.2004;Lagache et al.2004).An important aspect of infrared galaxy spectral en-ergy distributions (SEDs)is the behavior between 3and 24μm,a range that includes emission from PAH (Poly-cyclic Aromatic Hydrocarbon)molecules and warm dust.At redshifts between 1and 3,the PAH features move through the MIPS 24um band.Ad hoc adjustments to this spectral region in SED models (Lagache et al.2004)have been required to ?t the 24μm number counts (Papovich et al.2004;Marleau et al.2004;Chary et al.2004).Liang et al.(2004)show that infrared luminous galaxies at z ～0.6are only ～50%as metal-rich as their local analogs.Therefore,interpreting the behavior of galaxies detected with Spitzer to substantially higher redshifts (e.g.,Per′e z-Gonz′a lez et al.2005,submitted to ApJ)depends critically on understanding the e?ects of metallicity on the 24μm ?ux densities for 1

1

Steward Observatory,University of Arizona,Tucson,AZ 85721;cengelbracht@https://www.sodocs.net/doc/6e12516925.html,

2Jet Propulsion Laboratory,MC 264-767,4800Oak Grove Drive,Pasadena,CA 91109

3Department of Physics and Astronomy,University of Wyoming,Laramie,WY 82071

4Spitzer Science Center,California Institute of Technology,Pasadena,CA 91125

despite 3decades of searching.Low-metallicity galaxies have had little or no star formation up to the present epoch and are therefore of very low luminosity.As a result,most existing compilations of the MIR proper-ties of galaxies are restricted to high-metallicity,high-luminosity targets (e.g.,Genzel et al.1998;Lu et al.2003).Where low-metallicity galaxy spectra have been obtained,though,they di?er dramatically from their higher-metallicity cousins in their infrared prop-erties,with hotter large-grain dust emission and weak PAH emission (Sauvage et al.1990;Calzetti et al.2000;Galliano et al.2003;Contursi et al.2000;Thuan et al.1999;Houck et al.2004b;Roche et al.1991;Madden 2002).

This work greatly expands the sample of low-metallicity galaxies observed in the infrared,to explore the e?ects of metallicity on the infrared properties of galaxies in a systematic way.The larger sample has al-lowed us to pinpoint the metallicity at which the transi-tion from weak to strong PAH emission occurs.

2.OBSERVATIONS AND DATA REDUCTION

The new data presented here were obtained using IRAC and MIPS.The IRAC data are all standard pipeline reductions using the most recent versions avail-able in the archive,ranging from 9.5.0to 10.5.0.The MIPS data were reduced using the MIPS DAT (Data Analysis Tool;Gordon et al.2005).

Photometry was performed using the “imexam”and “imstat”tasks in IRAF 5.Most sources in the sample are compact;in general,apertures large enough to encom-pass all the ?ux were used for MIPS,while the stan-dard aperture with a radius of 10pixels (12′′)was used for IRAC,as suggested in the IRAC data handbook.For the extended galaxies,matching apertures that in-clude the whole galaxy were used for MIPS and IRAC,and extended-source corrections have been applied to

5

IRAF is distributed by the National Optical Astronomy Ob-servatories,which are operated by the Association of Universities for Research in Astronomy,Inc.,under cooperative agreement with the National Science Foundation.

2

the IRAC measurements as described in the IRAC data handbook.No color corrections were applied,which should not have a strong impact on the results since the corrections listed in the IRAC and MIPS handbooks are typically only a few percent.

To increase the number of metal-rich galaxies in the sample,we have supplemented our measurements with results from the literature.Where IRAC and MIPS mea-surements were available,they have been taken directly from the sources indicated in Table1.We have synthe-sized IRAC and MIPS measurements from an IRS(In-frared Spectrograph;Houck et al.2004a)measurement of NGC7714by Brandl et al.(2004)by convolving the spectrum with the IRAC8μm and MIPS24μm spectral response curves available on the SSC(Spitzer Science Center)website.

Finally,we have added several measurements from MSX(Midcourse Space Experiment)by Kraemer et al. (2002)and IRAS(Infrared Astronomical Satellite)by Rice et al.(1988).The MSX Band A(8.28μm)and IRAC8μm?ux densities measured for two galaxies (M101,K.Gordon,in preparation;M83,C.Engel-bracht,in preparation)are very similar(within20%in both cases),so we have made no correction to the MSX measurements used in this paper.We have made an empirical color correction from the IRAS25μm band to the MIPS24μm band by comparing the measured ?ux densities of NGC7331(Regan et al.2004),M81 (Gordon et al.2004),NGC55(Engelbracht et al.2004), and M101(K.Gordon,in preparation).The measured 24μm to25μm ratios ranged from0.81to0.94,so we applied the average value,0.87,to all the IRAS mea-surements incorporated into the?ux density ratio mea-surements in Table1.

The resulting sample is a heterogeneous collection of star-forming galaxies without strong active nuclei. The global photometry measurements make this sample suitable for comparison to high-redshift samples(e.g., Fazio et al.2004),where only?ux measurements inte-grated over the whole galaxy are feasible.The metallic-ity quoted for each galaxy generally applies to a much smaller beam than for the infrared data.The outer re-gions of each galaxy should have lower metallicity than the nuclei.Thus,the beam mismatch would,if anything, weaken the trend of infrared properties we see clearly in the suite of measurements.We conclude it is not an im-pediment to this study.

3.RESULTS

To explore the contribution of PAH emission to the 8μm band,we compare the8μm measurements to bands at both shorter and longer wavelengths.The longer-wavelength24μm band is already dominated by emis-sion by dust and so we use it directly,but the shorter-wavelength5.8and4.5μm bands can contain signi?cant contributions from PAH emission and starlight,respec-tively.To avoid contamination from PAH features,we do not use the5.8μm band to derive the dust contin-uum measurement.We instead use the4.5μm band,from which we subtract the stellar component as follows:We assume the3.6μm band is dominated by starlight(which may result in an underestimate of the4.5μm dust emis-sion by a few percent;cf.Helou et al.2004)and mul-tiply the3.6μm measurement by the4.5/3.6μm ratio expected for the stellar population,derived from Star-burst99(Leitherer et al.1999)data?les available on the web6.The ratio predicted by that model is typically0.53 to0.61,depending on star formation history and metal-licity.We adopt the average value of0.57and assign to it an uncertainty of7%.Hereafter,we refer to this ratio as α.Our adopted value ofαis similar,but not identical to, the value of0.47in the template elliptical galaxy spec-trum used by Lu et al.(2003)to measure the hot dust component in a sample of galaxies.This will have some e?ect on our measurement of the4.5μm dust component for speci?c galaxies but does not a?ect the conclusions we draw from a diagnostic plot,as we discuss below.The scaled3.6μm measurement is then subtracted from the 4.5μm measurement.For the galaxies in this sample,the scaled3.6μm measurement ranges from26%to96%of the4.5μm measurement,with an average value of70%. We did not subtract the stellar contribution from the 8μm and24μm measurements because the correction is small for these galaxies and has no impact on our https://www.sodocs.net/doc/6e12516925.html,ing the same Starburst99models as above,we derive that the stellar contribution at8μm ranges from 1%to30%with an average of10%and the contribution at24μm is negligible,less than1%on average.

The8μm measurements compared to the short and long wavelength bands are summarized in Table1,where the ratio to the4.5μm band is referred to as R1and the ratio to the24μm band as R2.Increasing levels of PAH emission will result in decreasing values of R1and in-creasing values of R2.We note that any correction for dust in the3.6μm band will tend to increase the cal-culated4.5μm dust emission and therefore increase the value of R1for those galaxies without strong PAH emis-sion.

The color measurements are presented graphically in Figure1.The?gure shows that galaxies with high values of R1tend to have low values of R2,while those galaxies with a value of R1in the range of0.01to0.09(similar to our galaxy;cf.Lu2004)tend to have larger values of R2,although with a large dispersion.We?nd that the separation of galaxies in this plot persists if we change our assumptions about how to compute the4.5μm dust continuum,e.g.,by changing the value ofαto0.47to match the value used by Lu et al.(2003)or by using near-infrared data(such as the J band,which should not have a contribution from hot dust)to determine the stellar contribution to the4.5μm band.This trend is consistent with the spectroscopic results summarized in the“PAH”column of Table1,which demonstrate that all the galaxies with spectra free of PAH emission cluster in the upper-left portion of the diagram.

To interpret these results,we used the SED models of Dale et al.(2001a).To compute photometry from the models(which do not contain a stellar emission com-ponent),we convolved them with the same spectral re-sponse curves discussed in§2.The various?ux density ratios were then computed as for the data.The emis-sion in the IRAC bands derived from these models is dominated by a?xed PAH spectral template,and as a result the models have a nearly constant value of R1, around0.025.The models cover a range of R2values that depends on the temperature of the thermally puls-6https://www.sodocs.net/doc/6e12516925.html,/science/starburst99/

Metallicity E?ects on MIR Galaxy Colors

3 Fig. 1.—MIR colors of galaxies with a range of metallicities.

The8μm band is compared to both shorter(4.5μm,with stellar

emission subtracted as described in the text)and longer(24μm)

wavelengths.Galaxies with known PAH features are indicated by

?lled markers,while galaxies known to lack PAH features are in-

dicated by open markers.Error bars include a10%relative cali-

bration uncertainty between the IRAC and MIPS instruments and

a7%uncertainty onα,in addition to photometric uncertainties.

The dashed line indicates our chosen separation between PAH and

non-PAH galaxies in this color space.The range of points covered

by the Dale et al.(2001a)SED models is shown as a solid line.

ing grains,along the locus of points outside the region to

the upper left occupied by the PAH-free galaxies.Thus,

the weakness of the8μm emission relative to the other

bands appears to be due to the weakness of the PAH

emission relative to the emission from small dust grains.

Figure2shows the8-to-24μm color vs.metallicity(the

solar metallicity on this scale is8.7;Allende Prieto et al.

2001).We label the galaxies according to the lack or

presence of8μm PAH emission using the color separation

from Figure1.They separate very cleanly according to

metallicity,with a narrow transition region around1/3to

1/5solar metallicity.One additional galaxy,NGC1569,

has been shown to have weak PAH emission(Lu et al.

2003)and has an O/H-based metallicity25%of solar,

consistent with this overall behavior.

The boundary between metallicities with and without

PAH emission is surprisingly sharp,and it seems likely

that future studies will show more scatter.For example,

there can be signi?cant variations in metallicity within

these systems(e.g.,a factor of three is indicated for

SBS0335-052;Houck et al.2004b).Our characterization

of this parameter with a single value is an oversimpli?-

cation.In addition,”metallicity”includes enrichment

of the ISM with a broad variety of elements,produced

in di?erent ways.Oxygen is produced predominantly in

very massive stars;use of other elements produced in

other ways as metallicity indicators may yield di?erent

behavior.Nonetheless,there is a robust trend toward

low PAH emission in galaxies with relatively unpolluted

ISMs.

Why do the PAH features become weaker in low-

metallicity galaxies?We reject extinction as a possible

cause,both because the e?ect would have to(counterin-

tuitively)become stronger in galaxies with lower heavy-

element abundance(and presumably less dust)and be-

cause the direct measurement of extinction in the low-

metallicity galaxy SBS0335-052shows it to be optically

Fig.2.—Galaxy metallicity as a function of the8to24μm color.

Galaxies with colors or spectra that indicate that they have8μm

PAH features are displayed as?lled markers,while galaxies which

lack the8μm PAH feature are shown as open markers.Squares

and circles denote measurements with and without spectroscopic

con?rmation,respectively.The error bars on the8/24μm ratio are

the same as in Figure1,while the error bars on the metallicity are

typically0.05or less(cf.Kobulnicky&Skillman1996)and were

all assigned an uncertainty of0.05.Note that this?gure does not

require IRAC data(some of the8μm measurements were made by

MSX)and thus contains more points than Figure1.

thin in the MIR(Houck et al.2004b).It is also un-

likely that starburst activity(i.e.,the intensity of the

star formation)is a major contributor to the e?ect:the

correlation coe?cient between R2and the24μm surface

brightness(an indicator of the speci?c star formation

rate,which we estimated from the integrated?ux den-

sities and the visible extent of the galaxies in the sam-

ple)is much lower than the correlation coe?cient be-

tween R2and the metallicity(0.26vs.0.79).Also,while

the well-known starburst galaxies in our sample(e.g.,

NGC253,NGC7714),do tend to have lower R2val-

ues than other galaxies at similar metallicity,none of

them have as small an R2value as the lowest metallic-

ity galaxies.One possible reason is the destruction of

the PAH carrier in the harsh radiation?eld of a low-

metallicity galaxy(Plante&Sauvage2002).Another

possibility is that these galaxies are truly young and

the PAH molecules have simply not had time to form

(Dale et al.2001b).For example,it is well known that

the ISM of a galaxy must be signi?cantly polluted with

oxygen(produced copiously in very massive stars)be-

fore signi?cant amounts of carbon are produced(by stars

of a few M⊙)—this e?ect may delay PAH production

(E.Dwek,private communication).The low-metallicity

galaxies may simply lack the carbon-rich AGB stars re-

quired to form the PAH molecules(Latter1991).

In addition,we?nd that the PAH features included

in the Dale et al.(2001a)models fail to account for the

high values of R1prevalent at low metallicity(i.e.,below

8.0).The emission by dust in the models below10μm is

several orders of magnitude lower than the emission from

the PAH template(which does not vary),so the simple

remedy to the models of weakening the PAH spectrum

does not allow them to match the low-metallicity data.

The value of R1derived from the model depends only

on the shape of the PAH template spectrum and does

not match the low-metallicity galaxies shown in Figure1

4

(i.e.,the model R1value plotted in Figure1does not shift as the PAH features are weakened).Some other source of emission must be dominating in these sources, such as hot dust in the4.5μm band(cf.Lu et al.2003).

4.CONCLUSIONS

We have combined new MIR measurements from the Spitzer Space Telescope with results from the literature to show that the8μm to24μm?ux density ratio in star-forming galaxies depends strongly on metallicity.The 8μm to24μm color changes markedly between1/3to1/5 solar metallicity—the mean ratio below1/3solar metal-licity is0.08±0.04,while the ratio at higher metallicity is0.70±0.53.A MIR color-color diagram which com-pares the8μm band to dust continuum measurements at 4.5and24μm shows that the change in the ratio is pre-dominantly due to a decrease in the8μm emission.We interpret this result as a weakening of the PAH features at low metallicity,an interpretation consistent with the spectroscopic evidence available in the literature.

We show that existing empirical SED models cannot account for the color change merely by weakening the PAH component of the models.In addition to the depen-dence of PAH strength on metallicity,SED models must account for another source of emission(e.g.,hot dust)to explain the IRAC observations of low-metallicity galaxy colors.

The shift in8to24μm ratio occurs at a fairly high metallicity and will thus a?ect the spectra of many galax-ies.Future SED models to interpret Spitzer measure-ments at high redshift must take the dependence of metallicity on redshift into account.

We thank Eli Dwek for helpful discussions,and Nanyao Lu and Eiichi Egami for comments which improved this paper.This work is based in part on observations made with the Spitzer Space Telescope,which is operated by the Jet Propulsion Laboratory,California Institute of Technology under NASA contract1407.Support for this work was provided by NASA through Contract Number 960785issued by JPL/Caltech.

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Metallicity E?ects on MIR Galaxy Colors5

TABLE1

Galaxy Colors and Metallicities

Galaxy fν(4.5μm)fν(24μm)R1a R2b Z c PAH d References

Jy Jy?ux densities e Z PAH I Zw18 3.4e-4 5.5e-30.180.127.2...12... SBS0335-052 1.5e-3 6.6e-20.100.177.3no134 HS0822+3542 1.45e-4 2.7e-30.400.067.4...15... Tol1214-2777.2e-5 5.5e-30.100.047.6...12... Tol65 3.6e-4 1.5e-20.210.067.6...12... Tol2138-405 2.4e-3 5.7e-20.130.157.6...16... VII Zw403 2.4e-3 2.8e-20.220.097.7...17... Mrk153 1.45e-3 2.9e-20.140.087.8no189 UM461 5.5e-4 3.0e-20.110.057.8...12... Haro11 3.2e-2 1.9e+00.100.107.9...110... NGC4861 3.2e-3 2.8e-10.140.037.9...111... Mrk14509.2e-4 4.8e-20.130.058.0...112... UM448 1.1e-2 5.6e-10.030.168.0yes1129 UM462 2.4e-3 1.1e-10.150.068.0...12... Mrk930 2.3e-3 1.7e-10.060.068.1no1129

II Zw40 1.1e-2 1.5e+00.060.078.1no1213 NGC4670 1.5e-2 2.1e-10.030.368.2...114... NGC1156... 4.5e-1...0.198.2...1516... NGC0598... 5.0e+1...0.508.5...17,1819... NGC3077 2.76e-1 1.5e+00.020.488.6...120... NGC3008.8e-1 2.3e+00.090.708.6...2119... NGC2537 4.1e-2 2.4e-10.020.628.7...122... NGC7714... 2.4e+0...0.148.7yes232023 NGC2782 3.8e-29.6e-10.020.368.8yes11424 NGC4194 6.5e-2 3.1e+00.030.258.8yes12025 NGC5457... 1.0e+1...0.688.8...2619... NGC3031 6.5e+0 4.4e+00.03 2.028.8...27,281929 He2-10 6.0e-2 4.9e+00.020.148.9yes11124 NGC253... 1.4e+2...0.288.9yes17,301931 NGC5055... 6.1e+0...0.779.0...17,3019... NGC73319.5e-1 3.6e+00.01 1.369.0yes321933 NGC224...9.4e+1... 1.709.0yes17,301934 NGC5236... 4.2e+1...0.509.1yes1,301929 NGC2903 1.2e-1 2.2e+00.020.509.3yes1119

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(32)Regan et al.(2004);(33)Smith et al.(2004);(34)Cesarsky et al.(1998).

a R1=[fν(4.5μm)?αfν(3.6μm)]/fν(8μm),whereαis as described in the text.

b R2=fν(8μm)/fν(24μm)

c12+log(O/H)

d Th

e PAH designation is based on results reported in the cited works or on visual inspection o

f the spectra.

e A single entry refers to both IRAC and MIPS measurements together.Two entries indicate separate sources for the measurements,with the IRAC reference followed by the MIPS reference.

大学生毕业晚会主持词

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毕业生晚会主持稿 毕业生晚会主持稿(一) A：青春是一曲荡气回肠的歌，三年前我们怀着彩色梦想走进了鄂大，三年中我们有过欢笑，流过泪水，经历磨炼，得到成长：三年后的今天，我们在这里重温青春过往，因为明天就将各奔天涯。也正因为此，今夜，我们承载了太多的祝福与惦念，寄托了太多的关怀与企盼。 C：今晚，让我们再一次重温，那些感动过我们的人和事：灯火通明的教学楼里用功的身影，篮球场上捍卫集体尊严的男儿霸气，满是欢声笑语的宿舍边不着边际的闲谈 D：又一个三年轮回之后，在同样微凉的夏夜，你是否会记起校园里的梧桐树，你是否会记起日记本里的书签，那些五彩缤纷的日子? A：无数个三年之后，你们的思念是否会有增无减?在你成长的岁月里，在你闯荡社会的每一天，是否会有那么几个瞬间让你渴望回到过去 ：让我们静静享受一下挑战，在日复一日与时间的赛跑中，你会变得更加坚强，更加神采奕奕!又一个青春之旅从今晚启航，又一个光阴的故事在今晚讲述 C：亲爱的同窗，不要带着离别的愁绪，因为明天又是一个新的起点，因为我们相信再次相逢，我们还是一首动人的歌!D：很

高兴今天能有这个机会同大家相聚一堂，共叙离别。就让今天铭刻在我们心间，让母校留住我们的风采! A：今天，我们也非常荣幸的请到了 ：下面让我们用热烈的掌声有请上台讲话 结束语A：欢快的舞蹈表达不尽我们对母校的敬意 ：热情的赞歌唱不尽我们对母校的一腔深情 C：流火的六月，我们将带着恩师的叮咛，怀着必胜的信心，走向新的征程 D：绚烂的七月，我们将载着母校的祝愿，带着亲人的希望，向着新的征程扬帆起航 A：老师们，同学们，欢送10级毕业生联欢晚会合：到此结束 A李：毕业，是一个沉重的动词; 刘：毕业，是一个让人一生难忘的名词; 李：毕业，是感动时流泪的形容词; 刘：毕业，是当我们以后孤寂时候，带着微笑和遗憾去回想时的副词; 李：毕业，是我们夜半梦醒，触碰不到而无限感伤的虚词。 刘：若干年后，假如我们还能够想起那段时光，也许这不属于难忘，也不属于永远，而仅仅是一段记录了成长经历的回忆。 李：尊敬的各位领导老师 刘：亲爱的各位同学们

大学生精彩毕业晚会主持词

大学生精彩毕业晚会主持词 大学生精彩毕业晚会主持词 A：六月、江畔的微风情深意暖，校园涌动的花海流溢飘香。 B：六月、想起毕业带来的奔忙，满怀即将失去的无限感伤。 C：六月、拾起曾经蕴藏的过往，体味相伴四年的欢欣成长。 D：六月、让你我懂得了珍惜，珍惜在校的每一段岁月流光。 A：毕业，是一沉重的动词，行动里带着眷恋与不舍。 B：毕业，是一难忘的名词，话语里带着心酸与苦涩。 C：毕业，是一流泪的形容词，不可或缺但又不能推辞。 D：毕业，是个遗憾的副词，历练成长却又让生活充实。 A：四年前，大家相遇相知，温暖胸膛、怀揣梦想。 B：四年里，大家共同努力，激越青春、欢乐成长。 C：四年后，即将天各一方，各自打造梦想的天堂。 D：朋友们，不要让泪水打湿容颜，火热激情即将绽放当晚，让我们的心于空中翱翔，在青春的蓬勃下生长，在岁月流光中温暖启航。 A：下面我宣布，20XX年师范学院青春启航文化节之毕业生晚会正式开始。 1.节奏引领时尚，余音环绕广场，新鲜的韵律，高难度的声响，一样为您缔造不一样的完美想象，下面请欣赏来自XX音乐班的xxx为您带来的《》相信会给您带来意外的惊喜。

2.铃声清脆鼓铿锵，天山铃舞尽展情，来自天山的自然是蝶飞花影动，美丽各不同，那就让我们停下脚步，一饱眼福，欣赏由xxx为我们带来的舞蹈《天山铃舞》 3. 军中有歌，歌才动情，军旅里飞来一只熟悉的百灵，不错下面就由请xxx为大家献上一首耳熟能详的老歌，《军中飞来一只百灵》 4.炫酷才叫时尚，八零后心之向往，相信大家都一样，需要个性张扬。今天我们特意请来了城市建设学院的武状元优秀团队，为大家献上一段充满活力的XXX，感谢他们的到来，大家掌声欢迎! 5.相信大家都看过一部曾经风靡一时的电影，那是周杰伦曾经推出的一部年度巨献《不能说的秘密》.里面的四手联弹一定给大家留下了不可磨灭的深刻印象，旋律依旧在脑中回响。不过经典一样可以复制，精彩一样能够粘贴，下面给大家带来的这个惊喜，可谓是非常具有特色，一样是所见不多，机会难得。下面请欣赏xxxx为大家带来的，钢琴四手连弹《军队进行曲》 6.幽幽云水意.漫漫古典情. 诗情画境的晕染为我们带来流动的娴静。请大家随着动人的舞蹈穿越书法的妙境，伴随优雅的琴韵体会超越喧嚣的古韵墨香。下面请欣赏xxx为您带来的xxxx 7.四年的岁月流光见证了你我在XX学院的欢欣成长，相信由很多即将走出校园的`同学都想倾诉衷肠，下面我们就请出来自05对外汉语的毕业生代表xxx听听她如何表达。

校园艺术节主持词开场白

校园艺术节主持词开场白（一） 男：尊敬的各位领导、各位来宾。 女：亲爱的老师们、同学们。 合：大家好！ 男：聆听十月的讯息，秋风吹拂大地； 女：走进十月的校园，我们充满活力！ 男：今天，我们相聚这儿，绽放灿烂的笑容；凝聚我们的勇气； 女：今天，我们相聚这儿，放飞我们的希望，追求我们的梦想！ 男：校园的艺术是知识的一种新的升华，校园的生活是多彩的音乐的合奏。 女：校园艺术节是师生展示各自文艺风采、凸显个性魅力的一个最佳舞台。 合：xx中学第x届校园艺术节开幕式现在开始！（鸣礼炮） 男：下面进行升旗仪式，请仪仗队入场。 女：请全体起立，升国旗、奏国歌！ 男：请大家入座。今天来到我们会场的领导有：xx、xx、xx…… 女：让我们用热烈的掌声对他们的到来表示欢迎！ 男：另外许多家长代表也来到了我们的会场，一个成功的学生背后总有辛勤付出的家长，您辛苦了！ 女：让我们用热烈的掌声对他们表示感谢！ 男：回首我们走过的这一个学年，经过全校师生上下一心、卓有成效的努力，我校各项工作都取得了骄人的成绩：校容校貌焕然一新，常规管理扎实有效，教学质量跃上新高。

女：成绩已然过去，面对未来，我们信心百倍。下面有请x校长讲话。 （鼓掌感谢x校长的精彩致辞） 环节一：教师合唱《走进新时代》、《团结就是力量》 男：我们xx人是这样的热情奔放！ 女：我们xx人是这样的团结激昂！ 男：我们的手牵在一起，就是战胜困难的力量！ 女：我们的心连在一起，就是坚不可摧的铜壁铁墙！ 男：让我们与优美同行，与高雅同行，与时代同行 女：请欣赏教师合唱《走进新时代》和《团结就是力量》。 指挥：xx 领唱：xx 环节二：舞蹈《开门红》 女：扬起你欢乐的嘴角，带上你的好心情，在这个特别的日子里跟我们一起感受这花样年华。

毕业典礼晚会主持词

毕业典礼晚会主持词X 花开花落，又是一年毕业季，我们毕业典礼就要开始举办，下面是搜集整理的毕业典礼晚会主持词，欢迎阅读。更多资讯请继续关注毕业典礼栏目! 毕业典礼晚会主持词(一) A：青春是一曲荡气回肠的歌，三年前我们怀着彩色梦想走进了鄂大，三年中我们有过欢笑，流过泪水，经历磨炼，得到成长 B：三年后的今天，我们在这里重温青春过往，因为明天就将各奔天涯。也正因为此，今夜，我们承载了太多的祝福与惦念，寄托了太多的关怀与企盼。 C：今晚，让我们再一次重温，那些感动过我们的人和事：灯火通明的教学楼里用功的身影，篮球场上捍卫集体尊严的男儿霸气，满是欢声笑语的宿舍边不着边际的闲谈…… D：又一个三年轮回之后，在同样微凉的夏夜，你是否会记起校园里的梧桐树，你是否会记起日记本里的书签，那些五彩缤纷的日子? A：无数个三年之后，你们的思念是否会有增无减?在你成长的岁月里，在你闯荡社会的每一天，是否会有那么几个瞬间让你渴望回到过去 B：让我们静静享受一下挑战，在日复一日与时间的赛跑中，你会变得更加坚强，更加神采奕奕!又一个青春之旅从今晚启航，又一个光阴的故事在今晚讲述 C：亲爱的同窗，不要带着离别的愁绪，因为明天又是一个新的起点，因为我们相信再次相逢，我们还是一首动人的歌!D：很高兴今天能有这个机会同大家相聚一堂，共叙离别。就让今天铭刻在我们心间，让母校留住我们的风采! A：今天，我们也非常荣幸的请到了…… B：下面让我们用热烈的掌声有请……上台讲话

结束语 A：欢快的舞蹈表达不尽我们对母校的敬意 B：热情的赞歌唱不尽我们对母校的一腔深情 C：流火的六月，我们将带着恩师的叮咛，怀着必胜的信心，走向新的征程 D：绚烂的七月，我们将载着母校的祝愿，带着亲人的希望，向着新的征程扬帆起航 A：老师们，同学们，欢送10级毕业生联欢晚会合：到此结束 A李：毕业，是一个沉重的动词; 刘：毕业，是一个让人一生难忘的名词; 李：毕业，是感动时流泪的形容词; 刘：毕业，是当我们以后孤寂时候，带着微笑和遗憾去回想时的副词; 李：毕业，是我们夜半梦醒，触碰不到而无限感伤的虚词。 刘：若干年后，假如我们还能够想起那段时光，也许这不属于难忘，也不属于永远，而仅仅是一段记录了成长经历的回忆。 李：尊敬的各位领导老师 刘：亲爱的各位同学们 合：大家晚上好! 李：很荣幸和大家相聚在这激情如火的六月，在这充满忧伤的六月! 刘：很高兴和大家相聚在“放心去飞，20年后再相聚—毕业晚会”现场! 李：我是李扬